Professor, Medicine - Clinical Pharmacology
We are interested in the general process of signal transduction, focusing on the role that ion channels play in this process. By means of path clamp recording and associated cell and molecular biological techniques, we have studied:
1. Voltage-insensitive Ca2+ channels, Ca2+-dependent K+ channels, other downstream Ca2+ dependent effector molecules; role in cellular activation and signal transduction.
2. Cystic fibrosis C1-channels in epithelial cells and lymphocytes; associated signal transduction pathways and cell biological coupling mechanisms. Phase I/II AAV-CFTR gene therapy trials.
3. NFAT mediated gene transcription; modulations by kinases and phosphatases.
Using the Hereditary Hearing Loss arrayed primer extension (APEX) array, which contains 198 mutations across 8 hearing loss-associated genes (GJB2, GJB6, GJB3, GJA1, SLC26A4, SLC26A5, 12S-rRNA, and tRNA Ser), we compared the frequency of sequence variants in 94 individuals with early presbycusis to 50 unaffected controls and aimed to identify possible genetic contributors. This cross-sectional study was performed at Stanford University with presbycusis samples from the California Ear Institute. The patients were between ages 20 and 65 yr, with adult-onset sensorineural hearing loss of unknown etiology, and carried a clinical diagnosis of early presbycusis. Exclusion criteria comprised known causes of hearing loss such as significant noise exposure, trauma, ototoxic medication, neoplasm, and congenital infection or syndrome, as well as congenital or pediatric onset. Sequence changes were identified in 11.7% and 10% of presbycusis and control alleles, respectively. Among the presbycusis group, these solely occurred within the GJB2 and SLC26A4 genes. Homozygous and compound heterozygous pathogenic mutations were exclusively seen in affected individuals. We were unable to detect a statistically significant difference between our control and affected populations regarding the frequency of sequence variants detected with the APEX array. Individuals who carry two mild mutations in the GJB2 gene possibly have an increased risk of developing early presbycusis.
View details for Web of Science ID 000260722000005
View details for PubMedID 18988928
In the Ashkenazi Jewish population, serious and lethal genetic conditions occur with relatively high frequency. A single test that encompasses the majority of population-specific mutations is not currently available. For comprehensive carrier screening and molecular diagnostic purposes, we developed a population-specific and inclusive microarray. The arrayed primer extension genotyping microarray carries 59 sequence variant detection sites, of which 53 are detectable bi-directionally. These sites represent the most common variants in Tay-Sachs disease, Bloom syndrome, Canavan disease, Niemann-Pick A, familial dysautonomia, torsion dystonia, mucolipidosis type IV, Fanconi anemia, Gaucher disease, factor XI deficiency, glycogen storage disease type 1a, maple syrup urine disease, nonsyndromic sensorineural hearing loss, familial Mediterranean fever, and glycogen storage disease type III. Several mutations in the selected disorders that are not prevalent per se in the Ashkenazi Jewish populations, as well pseudodeficiency alleles, are also included in the array. The initial technical evaluation of this microarray demonstrates that it is comprehensive, robust, sensitive, specific, and easily modifiable. This cost-effective array is based on a diversely applied platform technology and is suitable for both carrier screening and disease detection in Ashkenazi and Sephardic Jewish populations.
View details for DOI 10.2353/jmoldx.2007.060100
View details for Web of Science ID 000245427600013
View details for PubMedID 17384215
The advent of universal newborn hearing screening in the United States and other countries, together with the identification of genes involved in the process of hearing, have led to an increase in both the need and opportunity for accurate molecular diagnosis of patients with hearing loss. Deafness and hearing impairment have a genetic cause in at least half the cases. The molecular genetic basis for the majority of these patients remains obscure, however, because of the absence of associated clinical features in approximately 70% (ie, nonsyndromic hearing loss) of patients, genetic heterogeneity, and the lack of molecular genetic tests that can evaluate a large number of mutations across multiple genes.We report on the development of a diagnostic panel with 198 mutations underlying sensorineural (mostly nonsyndromic) hearing loss. This panel, developed on a microarray, is capable of simultaneous evaluation of multiple mutations in 8 genes (GJB2, GJB6, GJB3, GJA1, SLC26A4, SLC26A5 and the mitochondrial genes encoding 12S rRNA and tRNA-Ser[UCN]).The arrayed primer extension array for sensorineural hearing loss is based on a versatile platform technology and is a robust, cost-effective, and easily modifiable assay. Because hearing loss is a major public health concern and common at all ages, this test is suitable for follow-up after newborn hearing screening and for the detection of a genetic etiology in older children and adults.Comprehensive and relatively inexpensive genetic testing for sensorineural hearing loss will improve medical management for affected individuals and genetic counseling for their families.
View details for DOI 10.1542/peds.2005-2519
View details for Web of Science ID 000240959100016
View details for PubMedID 16950989
This is a review of the application of microfabrication technologies, borrowed from the semiconductor industry, to drug delivery implants incorporating structures in the nanometer dimension. In the futuristic ideal, these systems would involve the implantation of precisely microfabricated drug delivery systems with nanopores, nanochannels and/or nanoreservoirs fabricated from silicon, coupled with electronic sensing and actuator systems, for the precise, timed and/or targeted delivery of drugs. After more than a decade in conceptualisation and experimentation, four systems that have commercial potential are discussed: i) implantable microchips with on-demand microdosage for one or more therapeutic agents under internal control or external control using a wireless link; ii) nanopore pumps, implantable titanium pumps, consisting of a drug reservoir with a nanopore-release membrane, capable of delivering potent small or macromolecules at constant serum levels for sustained periods of time; iii) nanocages, microfabricated nanopore immunoisolation chambers for cellular implants, capable of natural feedback-controlled delivery of proteins and peptides; and iv) nanobuckets, micromachined silicon porous particles with drug-loading capacity and targeting ligands for localised delivery. Each of the systems, along with future trends in microfabrication manufacturing, limitations and possibilities, are discussed.
View details for PubMedID 16822223
Hearing loss has a genetic etiology in the majority of cases and is very common. The universal newborn hearing screening program, together with remarkable recent progress in the characterization of genes associated with the function of hearing, have resulted in increased demand and exciting possibilities of detecting the molecular basis of hereditary hearing loss through DNA testing. Future molecular diagnostic assays are expected to offer a greater variety of gene-specific tests, as well as combined mutation panels, which will aid in the management of the impressive genetic heterogeneity observed in hereditary hearing loss, especially in individuals with nonsyndromic forms. This review addresses the genetics of hearing loss, discusses the most commonly offered genetic assays for nonsyndromic hearing loss, with advantages and limitations, proposes a practical testing algorithm, and highlights current developments.
View details for DOI 10.1586/14737220.127.116.115
View details for Web of Science ID 000237916000010
View details for PubMedID 16706740
Cystic fibrosis (CF), which is due to mutations in the cystic fibrosis transmembrane conductance regulator gene, is a common life-shortening disease. Although CF occurs with the highest incidence in Caucasians, it also occurs in other ethnicities with variable frequency. Recent national guidelines suggest that all couples contemplating pregnancy should be informed of molecular screening for CF carrier status for purposes of genetic counseling. Commercially available CF carrier screening panels offer a limited panel of mutations, however, making them insufficiently sensitive for certain groups within an ethnically diverse population. This discrepancy is even more pronounced when such carrier screening panels are used for diagnostic purposes. By means of arrayed primer extension technology, we have designed a genotyping microarray with 204 probe sites for CF transmembrane conductance regulator gene mutation detection. The arrayed primer extension array, based on a platform technology for disease detection with multiple applications, is a robust, cost-effective, and easily modifiable assay suitable for CF carrier screening and disease detection.
View details for Web of Science ID 000231054600008
View details for PubMedID 16049310
Characterization of CFTR mutations in the U.S. Hispanic population is vital to early diagnosis, genetic counseling, patient-specific treatment, and the understanding of cystic fibrosis (CF) pathogenesis. The mutation spectrum in Hispanics, however, remains poorly defined. A group of 257 self-identified Hispanics with clinical manifestations consistent with CF were studied by temporal temperature gradient electrophoresis and/or DNA sequencing. A total of 183 mutations were identified, including 14 different amino acid-changing novel variants. A significant proportion (78/85) of the different mutations identified would not have been detected by the ACMG/ACOG-recommended 25-mutation screening panel. Over one third of the mutations (27/85) occurred with a relative frequency >1%, which illustrates that the identified mutations are not all rare. This is supported by a comparison with other large CFTR studies. These results underscore the disparity in mutation identification between Caucasians and Hispanics and show utility for comprehensive diagnostic CFTR mutation analysis in this population.
View details for Web of Science ID 000228736900018
View details for PubMedID 15858154
tgAAVCF, an adeno-associated cystic fibrosis transmembrane conductance regulator (CFTR) viral vector/gene construct, was administered to 23 patients in a Phase II, double-blind, randomized, placebo-controlled clinical trial. For each patient, a dose of 100,000 replication units of tgAAVCF was administered to one maxillary sinus, while the contralateral maxillary sinus received a placebo treatment, thereby establishing an inpatient control. Neither the primary efficacy endpoint, defined as the rate of relapse of clinically defined, endoscopically diagnosed recurrent sinusitis, nor several secondary endpoints (sinus transepithelial potential difference [TEPD], histopathology, sinus fluid interleukin [IL]-8 measurements) achieved statistical significance when comparing treated to control sinuses within patients. One secondary endpoint, measurements of the anti-inflammatory cytokine IL-10 in sinus fluid, was significantly (p < 0.03) increased in the tgAAVCF-treated sinus relative to the placebo-treated sinus at day 90 after vector instillation. The tgAAVCF administration was well tolerated, without adverse respiratory events, and there was no evidence of enhanced inflammation in sinus histopathology or alterations in serum-neutralizing antibody titer to adeno-associated virus (AAV) capsid protein after vector administration. In summary, this Phase II trial confirms the safety of tgAAVCF but provides little support of its efficacy in the within-patient controlled sinus study. Various potentially confounding factors are discussed.
View details for Web of Science ID 000177015400009
View details for PubMedID 12162817
The host immune response and low vector efficiency have been key impediments to effective cystic fibrosis transmembrane regulator (CFTR) gene transfer for cystic fibrosis (CF). An adeno-associated virus vector (AAV-CFTR) was used in a phase I dose-escalation study to transfer CFTR cDNA into respiratory epithelial cells of the maxillary sinus of 10 CF patients.A prospective, randomized, unblinded, dose-escalation, within-subjects, phase I clinical trial of AAV-CFTR was conducted.Ten patients with previous bilateral maxillary antrostomies were treated.Safety, gene transfer as measured by semiquantitative polymerase chain reaction (PCR), and sinus transepithelial potential difference (TEPD) were measured.The highest level of gene transfer was observed in the range of 0.1-1 AAV-CFTR vector copy per cell in biopsy specimens obtained 2 weeks after treatment. When tested, persistence was observed in one patient for 41 days and in another for 10 weeks. Dose-dependent changes in TEPD responses to pharmacologic intervention were observed following treatments. Little or no inflammatory or immune responses were observed.AAV-CFTR administration to the maxillary sinus results in successful, dose-dependent gene transfer to the maxillary sinus and alterations in sinus TEPD suggestive of a functional effect, with little or no cytopathic or host immune response. Further study is warranted for AAV vectors as they may prove useful for CFTR gene transfer and other in vivo gene transfer therapies. A prospective, randomized, double-blind, placebo-controlled, within-subjects, phase II clinical trial of the effect AAV-CFTR on clinical recurrence of sinusitis will determine the clinical efficacy of AAV gene therapy for CF.
View details for Web of Science ID 000078432500017
View details for PubMedID 10890777
Assessing the biological activity and clinical efficacy of gene therapy is critically important in cystic fibrosis (CF). It is widely accepted that clinical testing using surrogate markers including pulmonary function will be useful in assessing clinical efficacy. One problem with pulmonary surrogate markers of CF disease is the large number of patients and length of time required to demonstrate clinical efficacy. An alternative to pulmonary testing of new CF treatments is use of the maxillary sinuses as a surrogate model of CF lung disease. Using CF sinusitis as a surrogate model for testing clinical efficacy of new treatments is attractive because CF upper respiratory disease is similar to the lower respiratory disease with respect to electrophysiology and microbiology.Sinusitis recurrence in untreated sinuses was analyzed during a prospective, randomized, unblinded, dose-escalation, within-subjects, phase I clinical trial of the adeno-associated virus mediated cystic fibrosis transmembrane conductance regulator (AAV-CFTR) gene transfer.Clinical symptoms combined with sinus endoscopy proved useful in the diagnosis of unilateral and bilateral sinusitis recurrence. Sinusitis recurred at a rate of 45% during one month of follow-up. IL-8 concentration rose in sinus fluids from affected sinuses. Bacterial cultures and increased sinus leukocytes corroborated recurrent sinusitis. Sinus CT scans were also useful in diagnosing recurrent sinusitis in this surrogate model of CF infectious exacerbations.CF sinusitis as a surrogate for lung disease is particularly well-suited for phase II clinical trials of gene transfer agents, with the potential for measuring clinical efficacy in relatively small numbers of patients over relatively short periods of time.
View details for Web of Science ID 000083463500002
View details for PubMedID 10738581
The intestinal tract has many features that make it an attractive target for therapeutic gene transfer. In this study, replication-defective adenoviral vectors were used to explore parameters that may be important in administering gene therapy vectors to the intestine. After surgically accessing the intestine, an E1-, E3-deleted adenoviral vector encoding beta-galactosidase (beta-Gal) was directly injected into various regions of the small and large intestine of rats and rabbits. Significant transduction of the tissue was observed and histochemical staining was used to identify enterocytes as the primary targets of gene transfer. Expression of beta-Gal did not differ substantially when the virus was administered to the duodenum, ileum, or colon. When the vector was directly administered to segments of the distal ileum containing a Peyer's patch, transgene expression was approximately 10-fold higher than in segments lacking a Peyer's patch. In the Peyer's patches, a high level of expression was localized to epithelial cells, potentially M cells, overlying the lymphoid follicle domes. Transduction of these cells could have application in DNA-mediated oral vaccination. Administration of an adenoviral vector encoding a secreted alkaline phosphatase to the lumen resulted in expression and secretion of this gene product into the circulation. This finding demonstrates the potential of enterocytes to serve as heterotopic sites for the synthesis of heterologous gene products that would be secreted into the lumen of the intestinal tract or into the bloodstream.
View details for Web of Science ID 000074207900007
View details for PubMedID 9650616
The transcription factor NF-AT responds to Ca2+-calcineurin signals by translocating to the nucleus, where it participates in the activation of early immune response genes. Calcineurin dephosphorylates conserved serine residues in the amino terminus of NF-AT, resulting in nuclear import. Purification of the NF-AT kinase revealed that it is composed of a priming kinase activity and glycogen synthase kinase-3 (GSK-3). GSK-3 phosphorylates conserved serines necessary for nuclear export, promotes nuclear exit, and thereby opposes Ca2+-calcineurin signaling. Because GSK-3 responds to signals initiated by Wnt and other ligands, NF-AT family members could be effectors of these pathways.
View details for Web of Science ID A1997WQ51300045
View details for PubMedID 9072970
Cystic fibrosis (CF) is a common genetic disorder characterized by defective epithelial chloride transport and progressive lung disease. Although great strides have been made in the treatment of CF, it remains lethal, often by early adulthood. CF is one of the most extensively researched genetic diseases as a target for gene therapy development. It may also serve as an important model for gene therapy of other diseases. Preclinical and clinical research has lead to the rapid development of a variety of vectors designed to correct the basic defect in CF, including adenovirus, adeno-associated virus, and liposomes. Clinical studies have identified the host immune response and low vector efficiency as key impediments to effective CF gene therapy. Further research promises to refine vector technology and bring CF gene therapy to the bedside.
View details for Web of Science ID A1997WH48600017
View details for PubMedID 9046956
Expression of the CFTR protein is thought to be physiologically important only in exocrine epithelial cells. However, chronic respiratory inflammation and infection remain unexplained phenomena in disease pathogenesis. Non-transformed, antigen-responsive CD4+ T cells cloned from healthy controls and CF patients homozygous or heterozygous for the delta F508 mutation transcribed CFTR mRNA and expressed immunoreactive cytoplasmic CFTR protein. T cell clones (TCC) from controls and CF patients displayed equivalent Ca(2+)-mediated Cl- current; however, TCC from patients with CF but not controls displayed defective cAMP-mediated Cl-current. Although CF-derived TCC preserved mitogen and antigen proliferative responses and specificity to tetanus toxoid epitopes, they selectively secreted approximately 45% less IL-10 compared with control TCC after activation with concanavalin A (Con A) (624 +/- 101 versus 1564 +/- 401 pg/ml per 10(6) cells, respectively; P = 0.04) or anti-CD3/phorbol ester (5148 +/- 1634 versus 11788 +/- 2390 pg/ml; P = 0.05). This difference was independent of atopy. Secretion of interferon-gamma, IL-2, and IL-4 was comparable in CF and control TCC after both forms of activation, while IL-5 was reduced in CF TCC following anti-CD3/phorbol myristate acetate (PMA) but not after Con A. We conclude that expression of mutant CFTR in human TCC is accompanied by ion channel dysfunction characteristic of the CF phenotype, and is accompanied by a reduction in IL-10 secretion after polyclonal activation. It is possible that disruption of IL-10-mediated anti-inflammatory homeostasis may contribute to early onset sustained inflammation in CF airways.
View details for Web of Science ID A1996VQ33800028
View details for PubMedID 8918588
Leflunomide, a novel immunosuppressive drug, prolongs experimental graft survival effectively and has been well tolerated in patients with rheumatoid arthritis. A77 1726, the active metabolite of leflunomide, inhibits lymphocyte proliferation in vitro. This study was conducted in Jurkat T cells to investigate the effects of A77 1726 on signal transduction pathways initiated by ligands of the T-cell receptor CD3 complex and to evaluate the effects of A77 1726 on nucleotide biosynthesis.Tritiated thymidine incorporation and cell counts quantitated cell proliferation. Spectrofluorescence of Indo/AM dye measured intracellular Ca2+ mobilization. A luciferase assay quantitated interleukin-2 gene promoter activity in stimulated cells transfected with an interleukin-2 promoter-luciferase gene construct. Pyrimidine and purine nucleosides were used to assess antagonism of the antiproliferative activity of A77 1726.(1) A77 1726 dose-dependently inhibited the proliferation of Jurkat T cells (inhibitory concentration of 50% = 6 mumol/L); (2) A77 1726 did not decrease mobilization of intracellular Ca2+ stimulated by phytohemagglutinin or anti-CD3 monoclonal antibody; (3) A77 1726 did not inhibit interleukin-2 gene promoter activity in cells stimulated with ionomycin plus phorbol myristate acetate; (4) inhibition of cell proliferation by A77 1726 was antagonized by addition of uridine, cytidine, or 2(+)-deoxycytidine; (5) addition of uridine 24 hours after treatment with A77 1726 antagonized inhibition of proliferation; (6) A77 1726 was not antagonized by 2'-deoxyuridine, thymidine, adenosine, or guanosine.(1) A77 1726 inhibited Jurkat T-cell proliferation without inhibiting T-cell receptor-mediated signal transduction events, including tyrosine kinase-dependent intracellular Ca2+ mobilization and activation of the interleukin-2 gene promoter; (2) the antiproliferative effects of A77 1726 on Jurkat T cells are primarily due to interruption of de novo pyrimidine nucleotide biosynthesis. These data provide evidence for a novel in vitro mechanism of the antiproliferative action of this immunosuppressant.
View details for Web of Science ID A1995TM55700002
View details for PubMedID 8719445
Microsomal Ca(2+)-ATPase inhibitors such as thapsigargin (THG), cyclopiazonic acid (CPA) and 2,5-di-(tert-butyl)-1,4-hydroquinone (DBHQ) have been shown to inhibit Ca2+ reuptake by the intracellular stores and increase cytosolic free Ca2+ ([Ca2+]i). DBHQ is a commercially available non-toxic synthetic compound chemically unrelated to THG and CPA. In this study, we tested the feasibility of utilizing DBHQ to improve Cl- secretion via the Ca(2+)-dependent pathway, in the cystic fibrosis (CF)-derived pancreatic epithelial cell line CFPAC-1. DBHQ stimulated 125I efflux and mobilized intracellular free Ca2+ in a dose-dependent manner. The maximal effects were seen at concentrations of 25-50 microM. DBHQ (25 microM) caused a short-term rise in [Ca2+]i in the absence of ambient Ca2+, and a sustained elevation of [Ca2+]i in cell monolayers bathed in the efflux solution (1.2 mM Ca2+), which was largely attenuated by Ni2+ (5 mM). Bath-application of DBHQ induced an outwardly-rectifying whole-cell Cl- current, which was abolished by pipette addition of BAPTA (5 mM) or CaMK [273-302] (20 microM), an inhibitory peptide of multifunctional Ca2+/calmodulin-dependent protein kinase (CaMKII). Pretreatment of monolayers of CFPAC-1 cells with DBHQ for 4-5 min significantly increased the Ca(2+)-independent or autonomous activity of CaMKII assayed in the cell homogenates. Thus, DBHQ appears to enhance Cl- channel activity via a Ca(2+)-dependent mechanism involving CaMKII. Pretreatment of CFPAC-1 cells with up to 50 microM DBHQ for 6 h did not cause any detectable change in cell viability and did not significantly affect the cell proliferation rate. These results suggest that appropriate selective microsomal Ca(2+)-ATPase inhibitors may be therapeutically useful in improving Cl- secretion in CF epithelial cells.
View details for Web of Science ID A1995RY95400014
View details for PubMedID 7560071
Nitric oxide, which is produced by cytokine-activated mononuclear cells, is thought to play an important role in inflammation and immunity. While the function of nitric oxide as a direct cytotoxic effector molecule is well established, its function as a transducer molecule in immune cells is not. By use of whole-cell patch clamp recordings, we show that nitric oxide activates cystic fibrosis transmembrane conductance regulator CI- currents in normal human cloned T cells by a cGMP-dependent mechanism. This pathway is defective in cystic fibrosis-derived human cloned T cells. These findings not only delineate a novel transduction mechanism for nitric oxide but also support the hypothesis that an intrinsic immune defect may exist in cystic fibrosis.
View details for Web of Science ID A1995RF90000002
View details for PubMedID 7540975
Cystic fibrosis (CF), a lethal disease common to Caucasians, is characterized by a defect in the CF transmembrane conductance regulator and the resulting defective cAMP-regulated Cl- secretion by epithelial cells. Clinical manifestations include both pancreatic and pulmonary insufficiency. Traditional therapeutic modalities address these problems with pancreatic enzyme replacement, vitamins and nutritional supplementation, antibiotics, and respiratory therapy. However, newer therapies directed at the specific underlying defects have emerged. In this review, we discuss agents that increase Cl- secretion via preserved Cl- secretory pathways, such as uridine triphosphate, or that enhance Na+ resorption, such as amiloride, thereby correcting altered airway secretions. We also discuss agents, including deoxyribonuclease (DNase), that directly reduce sputum viscosity. CF is an early target for in vivo gene therapy, since it is a monogenic autosomal recessive disease in which restoration of normal cAMP-regulated Cl- conductance can be achieved by complementation with a normal gene. The early clinical gene therapy therapy work, with gene introduction by both viral and nonviral vectors, is discussed.
View details for Web of Science ID A1995QV29100011
View details for PubMedID 7598494
1. By use of whole cell patch-clamp and Indo-1 fluorescence studies of the Jurkat T leukaemic cell line, we show that the new organic antagonist of receptor-mediated Ca2+ entry, SK&F 96365, inhibits the T cell Ca2+ current in a dose-dependent fashion, with an IC50 of 12 microM. 2. SK&F 96365 also inhibits [3H]-thymidine incorporation and interleukin-2 (IL-2) synthesis in peripheral blood lymphocytes. 3. SK&F 96365 has no effect on Ca2+ stores release or K+ channels. 4. This is the first account of an organic inhibitor of the T cell Ca2+ current. The ability of SK&F 96365 to inhibit IL-2 synthesis and cell proliferation suggests that a new class of related Ca2+ channel blockers can be developed as immunosuppressive agents.
View details for Web of Science ID A1994PN23700032
View details for PubMedID 7858878
It has been suggested that P-glycoprotein (P-gp), an ATP-dependent transporter responsible for classical multidrug resistance, is also a volume-regulated chloride channel. We reexamined this hypothesis by use of whole-cell patch clamp recordings of three matched pairs of cell lines, which were either drug-sensitive or drug-resistant due to P-gp overexpression. We demonstrate here that volume-regulated chloride-selective currents can be induced in cells with or without P-gp expression. Overexpression of either P-gp or cystic fibrosis transmembrane conductance regulator, the protein product of the CF gene and another member of the ATP-dependent transporters, is associated with a hypotonicity-induced, rapid onset, transient current prior to onset of the volume-sensitive chloride-selective current, an apparent nonspecific effect related to the overexpression of an integral membrane protein. These results suggest that there is no relationship between P-gp and the chloride channel activated by cell swelling.
View details for Web of Science ID A1994PH77400001
View details for PubMedID 7923110
In the presence of costimulation, Ca2+ influx in T cells leads to activation (transcription of interleukin-2; ref. 2) via calcineurin. In the absence of costimulation, Ca2+ influx results in anergy (interleukin-2 transcriptional block) through an unknown mechanism. Specific attenuation of interleukin-2 transcriptional induction occurs in Jurkat T cells following pretreatment with a Ca2+ ionophore. A > 90% block of inducible interleukin-2 reporter gene activity was initiated by transfection of a constitutively active mutant of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase or CaM kinase II), but not by constitutive mutants of CaM kinase IV, calcineurin or protein kinase C. The block was complete six hours after kinase transfection and showed specificity for interleukin-2; there was no change in beta-actin transcription or in c-fos transcription induced by phorbol myristyl acetate, and a Rous sarcoma virus promoter was stimulated threefold. Multifunctional CaM kinase also attenuated interleukin-2 activation by calcineurin plus phorbol ester. T-cell receptor signalling activates multifunctional CaM kinase. These findings suggest that two Ca2+/calmodulin-responsive enzymes, multifunctional CaM kinase and calcineurin, could mediate the divergent effects of Ca2+ signals in T-lymphocyte regulation.
View details for Web of Science ID A1994PH25400057
View details for PubMedID 8090206
The mechanism of TCR-stimulated Ca2+ influx was studied in the Jurkat human T cell line using Ca2+ indicator dyes and whole-cell patch clamp. Ca2+ influx induced by inositol 1,4,5-triphosphate (IP3)-coupled surface receptors (either the TCR or a heterologous muscarinic receptor) was compared with Ca2+ influx induced by inhibitors of the microsomal Ca(2+)-ATPase (thapsigargin, cyclopiazonic acid, di-tert-butylhydroquinone), which release stored Ca2+ without production of IP3. The same Ca2+ influx pathway could be activated by IP3-dependent or IP3-independent means, and therefore appeared to be regulated by the fullness of the microsomal Ca2+ stores rather than by the direct action of IP3. Depletion of stored Ca2+ by either receptor stimulation or microsomal Ca(2+)-ATPase inhibition activated a low conductance, Ca(2+)-selective, non-voltage-activated membrane current. Ca2+ currents induced by receptor stimulation and Ca(2+)-ATPase inhibition were not additive. Several properties of the depletion-activated Ca2+ current suggest that it is carried by a novel type of Ca2+ channel rather than an electrogenic carrier or pump. The conductance saturated when external Ca2+ was raised (Kd approximately 2 mM) and became highly permeable to monovalent cations when external Ca2+ was lowered to below 100 nM, much as has been observed for some voltage-gated Ca2+ channels. The Ca2+ current was reversibly blocked by > 90% with 0.3 mM Cd2+, whereas the same concentration of Ni2+ or Co2+ blocked only 50 to 60% of the current. However, the absence of voltage-dependent activation, relative conductance sequence for divalent cations (Ca2+ > Ba2+ approximately Sr2+ > Mn2+), and lack of inhibition by nifedipine, D600, diltiazem, delta-conotoxin, or aga-IVa were unlike that of voltage-gated Ca2+ channels.
View details for Web of Science ID A1994NM61500008
View details for PubMedID 8189045
1. P1 purinoceptor agonists like adenosine have been shown to stimulate Cl- transport in secretory epithelia. In the present study, we investigated whether P1 agonist-induced Cl- secretion is preserved in cystic fibrosis airway epithelium and which signalling mechanism is involved. The effects of purinoceptor agonists on Cl- secretion were examined in a transformed cystic fibrosis airway phenotype epithelial cell line, CFPEo-. 2. Addition of adenosine (ADO; 0.1-1 mM) markedly increased 125I efflux rate. The rank order of potency of purinoceptor agonists in stimulating 125I efflux was ADO > AMP > ADP approximately equal to ATP. A similar order of potency was seen in transformed cystic fibrosis nasal polyp cells, CFNPEo- (ADO > ATP > AMP > ADP). These results are consistent with the activation of Cl- secretion via a P1 purinoceptor. 3. The P1 agonists tested (at 0.01 and 0.1 mM) revealed a rank order of potency of 5'-N-ethylcarboxamine adenosine (NECA) > 2-chloro-adenosine (2-Cl-ADO) > R-phenylisopropyl adenosine (R-PIA). 4. The known potent A2 adenosine receptor (A2AR) agonist, 5'-(N-cyclopropyl) carboxamidoadenosine (CPCA, 2 microM) but not the A1 adenosine receptor agonist, N6-phenyl adenosine (N6-phenyl ADO, 10 microM) markedly increased 125I efflux rate (baseline, 5.9 +/- 2.0% min-1, + CPCA, 10.9 +/- 0.6% min-1; P < 0.01). The stimulant effect of CPCA (10 microM) was abolished by addition of the A2AR antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (100 microM; reported K(i) = 11 +/- 3 microM). These results favour the involvement of A2AR. 5. ADO (0.1-mM) and CPCA (2 microM) both induced a marked increase in intracellular [Ca2+] ([Ca2+]i); the effect of the latter was again abolished by pretreatment of the cells with DMPX. By contrast, N6-phenyl ADO did not affect [Ca2+]i. 6. In patch-clamp experiments, ADO (1 mM) induced an outwardly-rectified whole-cell Cl- current (baseline, 2.5 +/- 0.8 pA pF-1, + ADO, 78.4 +/- 23.8 pA pF-1; P < 0.02), which was largely inhibited in cells internally perfused with a selective inhibitory peptide of the multifunctional Ca2+/calmodulin-dependent protein kinase, CaMK [273-302] (20 microM), as compared to a control peptide, CaMK [284-302]. Addition of BAPTA (10 mM), a Ca2+ chelator, to the perfusion pipette also abolished the ADO-elicited Cl- current. 7. In conclusion, our results suggest that A2AR participates in regulation of airway C1 secretion via aCa2+-dependent signalling pathway, which involves CaMK and appears to be at least partially conserved in cystic fibrosis airway epithelial cells.
View details for Web of Science ID A1994NH08400029
View details for PubMedID 8032638
Heat-stable enterotoxins (STa) produced by pathogenic bacteria induce profound salt and water secretion in the gut, leading to diarrhea. Recently, guanylin, an endogenous peptide with properties similar to STa, was identified. While STa and guanylin bind to the same receptor guanylyl cyclase and raise cell cGMP, the signaling mechanism distal to cGMP remains controversial. Here we show that STa, guanylin and cGMP each activate intestinal Cl- secretion, and that this is abolished by inhibitors of cAMP-dependent protein kinase (PKA), suggesting that PKA is a major mediator of this effect. These agents induce Cl- secretion only in cells expressing the wild-type CFTR, indicating that this molecule is the final common effector of the signaling pathway. The involvement of CFTR suggests a possible cystic fibrosis heterozygote advantage against STa-induced diarrhea.
View details for Web of Science ID A1994NA28800008
View details for PubMedID 7510634
Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a mediator of calcium signals in diverse signaling pathways. In human lymphocytes and epithelial tissues, CaM kinase activates a chloride channel via a Ca(2+)-dependent pathway which is preserved in cystic fibrosis. To characterize the CaM kinase present in these tissues we have cloned an isoform of this kinase from human T lymphocytes. We show the cDNA structure of two variants of this human CaM kinase, gamma B and gamma C, which are predicted to translate to 518 and 495 amino acids, respectively. Amino acid differences between these isoforms and the rat brain gamma isoform (which we refer to as gamma A) are localized to the variable domain. We used RNase protection of this variable region to reveal the level of expression of gamma B and gamma C CaM kinase mRNAs in nine human tissues and cell lines. When transfected into Jurkat T cells, the gamma B cDNA encoded a functional kinase which cosedimented on sucrose gradients with endogenous T cell CaM kinase activity and formed a large multimeric enzyme. The recombinant gamma B isoform displayed two phases of autophosphorylation characteristic of CaM kinases, including the phase which converts it to a partially Ca(2+)-independent species. Site-directed mutagenesis of the predicted autoinhibitory domain yielded a mutant which was approximately 37% active in the absence of Ca2+/calmodulin, confirming the region as critical for autoregulation, and suggesting this mutant as a tool for studying the role of CaM kinase in nonneuronal tissues.
View details for Web of Science ID A1993KR82200022
View details for PubMedID 8449910
Sustained elevation of intracellular Ca2+ by cell surface receptors is often dependent on influx of Ca2+ across the plasma membrane through routes not involving voltage-gated Ca2+ channels. We demonstrate that intracellular release of inositol 1,4,5-trisphosphate (InsP3), either from stimulation of transfected human muscarinic receptors or from photolytic release of caged InsP3, activates whole cell Ca2+ current in the Jurkat T cell line. Whole cell voltage clamp recordings indicate that the current is carried by a Ca(2+)-selective channel that resembles T-type voltage-gated Ca2+ channels in relative conductance of different cation species. Elevation of internal Ca2+ inactivates the channel, whereas internal perfusion with inositol 1,3,4,5-tetrakisphosphate (InsP4) does not affect it. Photolytic release of caged 1-(alpha-glycerophosphoryl)-inositol 4,5-bisphosphate, an analog of InsP3 which activates InsP3 receptors but is not readily metabolized to InsP4, also activates the current. We conclude that generation of InsP3 is sufficient to activate Ca(2+)-selective channels in the plasma membrane of T cells. InsP3 may have its effect indirectly through depletion of Ca2+ stores, or directly with a plasma membrane-associated InsP3 receptor.
View details for Web of Science ID A1993KN53300018
View details for PubMedID 8382682
The role of calcium in the action of tumor necrosis factor (TNF) on human neutrophils is not clear. With fluorescent cytometry, using the visible wavelength calcium probe, fluo-3, and patch clamping, we investigated whether TNF induces cytosolic free Ca2+ changes and Ca(2+)-activated Cl- current, respectively. Bath application of 1000 units/ml recombinant human TNF alpha (rhTNF alpha) induced a rise in cytosolic free Ca2+ in 75% of fluo-3-loaded cells, 25% of which displayed irregular patterns of oscillation. Addition of rhTNF alpha activated Cl- current in 80% of tested cells; the activated current was blocked by 10 microM 5-nitro-2-3-phenylpropylamino)benzoic acid, a Cl- channel blocker. The current was similarly activated by 1 microM ionomycin, a Ca2+ ionophore. To study the mechanism by which rhTNF alpha induced Ca(2+)-activated Cl- current, we examined the involvement of calcium/calmodulin-dependent protein kinase (CaM kinase). With intracellular application of the Ca2+ chelator 1,2-bis (2-aminophenoxy)ethane-N,N,N',N'-tetraacetate (5 mM), the calmodulin antagonist (2 microM), CaM kinase II-(290-309), or the inhibitory peptide (10 microM), CaM kinase II-(273-302), the current was no longer activated by rhTNF alpha. The intracellular application of the control peptide (10 microM), CaM kinase II-(284-302), or the protein kinase C (PKC) inhibitory, PKC-(19-36), or control, [Glu27]PKC-(19-36), peptide (5 microM) did not block the rhTNF alpha-induced Cl- current. These results show that Ca2+ changes are associated with the effects of rhTNF alpha and that CaM kinase plays a role in the mechanism underlying rhTNF alpha-induced activation of Ca(2+)-activated Cl- current in human neutrophils.
View details for Web of Science ID A1993KH62000095
View details for PubMedID 8380590
There have been major advances over the last several years in understanding the molecular basis of signaling by the T lymphocyte (T-cell) antigen receptor. In this article we discuss the early phases of T-cell activation with an emphasis on receptor-associated signaling molecules, mobilization of Ca, and on the possible roles of Ca in signal transduction. Ligation of the extracellular domains of the T-cell receptor activates receptor-associated tyrosine kinases that can phosphorylate the gamma-isoform of phospholipase C, increasing its catalytic activity. This leads to production of inositol 1,4,5-trisphosphate, release of stored intracellular Ca, and activation of Ca-permeable plasma membrane channels. Many of the critical T-cell signal transducing enzymes such as phospholipase C and protein kinase C contain intrinsic Ca-binding domains, but for the most part the rise in cytoplasmic Ca is transduced by specialized Ca-binding proteins that lack catalytic domains. The Ca-binding proteins found in T-cells include members of both the EF-hand and annexin families, as well as other types of Ca-binding proteins. In T-cells, a number of important kinases, phosphatases, and cytoskeleton-modulating enzymes are functionally Ca dependent but have no Ca-binding domains and therefore must sense changes in the cytoplasmic Ca level through interactions with Ca-binding proteins.
View details for Web of Science ID A1992KF37500001
View details for PubMedID 1282295
Phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) by cAMP-dependent protein kinase leads to chloride flux in epithelial cells. Is CFTR also required for the calcium-dependent activation of chloride channels? We used antisense oligodeoxynucleotides to CFTR to reduce the expression of CFTR in colonic and tracheal epithelial cells. The antisense oligomers were a pair of adjacent 18-mers complementary to nucleotides 1-18 and 19-36 of CFTR mRNA. Sense and misantisense oligomers served as controls. A 48-h antisense treatment reduced the expression of CFTR protein as assayed by immunoprecipitation and autoradiography to 26% of the level in sense-treated T84 cells. Whole-cell patch clamp revealed that a 48-h antisense treatment of T84 and 56FHTE-8o- fetal tracheal epithelial cells reduced the cAMP-activated chloride current to approximately 10% of that in sense-treated cells. The half-life of functional CFTR is less than 24 h in these cells. In contrast, the calcium-activated chloride current was not affected by antisense treatment. Hence, the cAMP and calcium pathways are separate. CFTR is required for the cAMP pathway but not for the calcium pathway.
View details for Web of Science ID A1992JF85600026
View details for PubMedID 1379720
Cystic fibrosis (CF) is the most common lethal genetic disease among Caucasians, primarily affecting epithelial tissues of the lung and gut. Mutations in a single gene, the cystic fibrosis transmembrane conductance regulator (CFTR), are responsible for this disease. Whether a physiological defect exists in the immune system of CF patients has remained controversial. A chloride ion transport defect has been described in human CF-derived lymphocytes; however, it has not been possible to detect CFTR mRNA in lymphocytes. We report here that normal human B-lymphoblasts display whole cell Cl- conductances induced by calcium-mediated pathways, volume regulation, and cAMP which are equivalent to currents described in epithelial cells. B-lymphoblasts from CF-affected humans demonstrated defective Cl- conductance regulation by cAMP but preserved regulation by calcium-mediated and volume regulation mechanisms. CFTR involvement in cAMP regulation of Cl- conductance in lymphocytes is further supported by our demonstration of the presence of appropriately spliced CFTR mRNA segments in human B and T lymphocytes as detected by an optimized reverse-transcription and polymerase chain reaction approach. The identity of the amplified products was confirmed by hybridization to CFTR-specific probes and DNA sequencing. Furthermore, the 3'-end of the gene was found in a T cell cDNA library. We conclude that CFTR mRNA is expressed in lymphocytes, consistent with the cAMP regulation of chloride transport present in normal lymphocytes but defective in CF-derived lymphocytes.
View details for Web of Science ID A1992HD15400067
View details for PubMedID 1371114
Patch-clamp studies have identified a cAMP-dependent Cl- conductance in lymphocytes that is defectively regulated in cystic fibrosis. In this study we used 125I efflux and whole-cell patch-clamp studies to investigate whether prostaglandin E1 (PGE1), an agonist that generates intracellular cAMP in Jurkat T lymphocytes, activates a Cl- conductance. Stimulation of T cells by externally applied PGE1 stimulated 125I efflux and activated a slowly developing membrane current. When external and internal Cl- were about equal, the current reversed at about zero mV, but when external Cl- was lowered from 157 to 7 mM the reversal potential shifted 75 mV in the positive direction, demonstrating that the current carrier was Cl-. In addition, the current was blocked by 10 microM 5-nitro-2(3-phenylpropylamino) benzoic acid (NPPB), a potent Cl- channel blocker. A membrane-permeable cAMP analog mimicked the effect of PGE1, whereas intracellular application of a cAMP antagonist Rp-cAMP blocked the effect of PGE1. Addition of purified catalytic subunit of cAMP-dependent protein kinase (PKA) plus ATP to the recording pipette also activated a similar current, whereas internally applied Walsh inhibitor, the synthetic peptide inhibitor of PKA, blocked the PGE1 effect. These results suggest that PGE1, acting through PKA, activates a Cl- current in Jurkat T cells.
View details for Web of Science ID A1991GP26900012
View details for PubMedID 1721593
Ion channels, and ion fluxes in general, appear to regulate a wide variety of processes important to lymphocyte function in normal and disease states. These include resting ionic homeostasis and the more complex signaling events involved in activation, proliferation, cytotoxic function, and volume regulation. The wider application of patch-clamp and microfluorimetry techniques to lymphocytes has helped to clarify some issues and raised many more. It seems likely that rapid progress will be made in our understanding of these areas through a combination of immunological, biochemical, and electrophysiological approaches.
View details for Web of Science ID A1991GF80400001
View details for PubMedID 1724452
cAMP kinase has been shown to mediate the cAMP pathway for regulation of Cl- channels in lymphocytes, but the mediator of an alternative, Ca2+ pathway has not been identified. We show here that Ca2+ ionophore activates Cl- currents in cell-attached and whole-cell patch-clamp recordings of Jurkat T lymphocytes, but this activation is not direct. The effect of Ca2+ ionophore on whole-cell Cl- currents is inhibited by a specific peptide inhibitor of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase). Furthermore, Cl- channels are activated in excised patches by purified CaM kinase in a fashion that mimics the effect of Ca2+ ionophore in cell-attached recordings. These results suggest that CaM kinase mediates the Ca2+ pathway of Cl- channel activation.
View details for Web of Science ID A1991FH80200006
View details for PubMedID 1849722
Cystic fibrosis is associated with defective regulation of apical membrane chloride channels in airway epithelial cells. These channels in normal cells are activated by cyclic AMP-dependent protein kinase and protein kinase C. In cystic fibrosis these kinases fail to activate otherwise normal Cl- channels. But Cl- flux in cystic fibrosis cells, as in normal cells, can be activated by raising intracellular Ca2+ (refs 5-10). We report here whole-cell patch clamp studies of normal and cystic fibrosis-derived airway epithelial cells showing that Cl- channel activation by Ca2+ is mediated by multifunctional Ca2+/calmodulin-dependent protein kinase. We find that intracellular application of activated kinase and ATP activates a Cl- current similar to that activated by a Ca2+ ionophore, that peptide inhibitors of either the kinase or calmodulin block Ca2(+)-dependent activation of Cl- channels, and that a peptide inhibitor of protein kinase C does not block Ca2(+)-dependent activation. Ca2+/calmodulin activation of Cl- channels presents a pathway with therapeutic potential for circumventing defective regulation of Cl- channels in cystic fibrosis.
View details for Web of Science ID A1991EZ66600057
View details for PubMedID 1705665
In both T- and B-lymphocyte activation, antigen receptor or mitogen stimulation results in phosphoinositide turnover, generation of InsP3 and diacylglycerol, and a sustained rise in intracellular Ca2+, from both intracellular Ca2+ stores release and enhanced transmembrane Ca2+ influx. There is also an associated K+ efflux and membrane hyperpolarization. Patch clamp studies in T and B cells have revealed the presence of several types of ion channels that apparently contribute to the ion fluxes and to the membrane potential changes associated with lymphocyte activation. Three types of T-cell channels are described in this review. First, patch clamp studies have revealed the presence of a nonvoltage-gated, Ca2+ permeable channel, the probability of whose opening increases upon exposure of the T cell to activating ligands. Enhanced opening probability appears to be mediated by the second messenger InsP3, implying that InsP3 is responsible for both intracellular Ca2+ stores release and enhanced transmembrane Ca2+ influx. Thus, the control of [Ca2+]i remains coupled to TCR/CD3 function. The Ca2+ permeable channel also undergoes a Ca2(+)-dependent inactivation process in an autoregulatory fashion. In addition, voltage-gated K+ channels, which closely resemble the delayed rectifier K+ channel of nerve and muscle, can be classified into three subtypes, according to their voltage dependence of activation, inactivation kinetics, and pharmacological sensitivity. The expression of the three K+ channel subtypes varies with the cell's developmental state and functional class. The voltage-activated K+ channel is postulated to have a role in mitogenesis, based on studies that demonstrate an increase in K+ channel amplitude in the 24-48 hr following mitogen stimulation, and on studies that demonstrate that K+ channel blockers inhibit mitogenesis in a dose-dependent manner with the same potency sequence for ion channel block. The precise functional role of the voltage-activated K+ channel remains to be determined. Finally, a Ca2(+)-activated K+ channel in T cells has recently been described. This channel presumably underlies the K+ efflux and membrane hyperpolarization that accompany the mitogen-induced increase in [Ca2+]i. Three channel types that may contribute to activation have also been described in B lymphocytes. In murine myeloma and hybridoma cells, a voltage-gated Ca2+ channel similar to Ca2+ channels in nerve, heart, and muscle is present. It is unclear whether or not this type of Ca2+ channel is present in straight B-cell lines.(ABSTRACT TRUNCATED AT 400 WORDS)
View details for Web of Science ID A1990DA09800009
View details for PubMedID 1693081
A prolonged (at least 2-4 hr) elevation of [Ca2+]i accompanies early T cell activation by TCR/CD3-specific ligands. Ca2+ is generally thought to be an essential second messenger for early activation, but the precise molecular events contingent upon the Ca2+ signal remain to be determined. The Ca2+ signal can be separated into an early transient peak due to InsP3-released Ca2+ from intracellular stores, and a sustained plateau due to altered transmembrane Ca2+ flux. Patch clamp studies have identified an InsP3-activated, Ca2+ permeable channel in the plasma membrane of T lymphocytes that may be responsible for the sustained elevation of [Ca2+]i during continuous TCR/CD3 occupancy. The Ca2+ signal can be further resolved at the level of the single cell into a series of repetitive oscillations between peak and trough levels with a period of 16-20 s. The oscillations may be part of a frequency-encoded signaling system. Several nonlinear internal feedback controls may contribute to the periodic nature of the Ca2+ signal: PKC-mediated phosphorylation of the CD3 gamma subunit, which is a feedback inhibitor of TCR/CD3 function; amplification of Ca2+ release from endoplasmic reticulum by a highly cooperative step in the opening of Ca2+ channels by InsP3, and Ca2+-dependent feedback enhancement of PLC function; autoregulatory negative feedback on Ca2+ influx by Ca2+, both by a direct effect on the plasma membrane Ca2+ channel and by induction of membrane hyperpolarization secondary to Ca2+-activated K+ efflux. In addition, several other internal feedback controls on TCR/CD3 function, by CD4-induced tyrosine-specific phosphorylation of the CD3 zeta subunit, or on the Ca2+ signal, by extracellular Cl- or by GM1 gangliosides, are also postulated. The question of whether a G protein couples TCR/CD3 to PI hydrolysis and to Ca2+ mobilization is unresolved, although some indirect evidence for the involvement of GTP binding proteins in T cell activation has recently been obtained with cholera toxin. There is also preliminary evidence that TCR/CD3 may structurally conform to G protein coupled receptors, i.e., having a core structure of seven alpha helical transmembrane spanning segments, a ligand recognition site, loci for regulatory phosphorylation, and a putative nucleotide binding site.
View details for Web of Science ID A1989AU52300004
View details for PubMedID 2676193
Modulation of the voltage-gated K+ conductance in T-lymphocytes by substance P was examined. Whole-cell recordings from JurkaT E6-1 human T-lymphocytes revealed two components of substance P action on the outward K+ current: (i) dose- and time-dependent reduction of current peak amplitude; and (ii) acceleration of the current inactivation rate. This action was blocked by substituting Cs+ for K+ in the recording pipette and by the substance P antagonist. [D-Arg1, D-Phe5, D-Trp7,9, Leu11]-substance P. As indicated by conductance-voltage relationship, the reduction in current peak amplitude as a result of substance P application was not due to a shift of the voltage dependence of the channel. Raising intracellular free calcium concentration from 2 to 200 nM reversed the reduction, induced by substance P, in current peak amplitude and disclosed an apparent desensitization towards the neuropeptide action. The treatment, however, did not reverse substance P-induced acceleration of the rate of current decay. Intracellular administration of hydrolysis-resistant guanosine triphosphate (to persistently activate GTP-binding protein) and guanosine diphosphate (to competitively inhibit GTP-binding proteins) analogues mimicked and inhibited substance P-induced reduction of K+ conductance, respectively. The data demonstrate a modulation of T-lymphocyte K+ channels by substance P and substantiate a possible role for GTP-binding proteins in this modulation.
View details for Web of Science ID A1989AX58900003
View details for PubMedID 2482361
A proteinaceous hemolysin secreted by strain 4074 of serotype 1 of Actinobacillus pleuropneumoniae was purified by diafiltration and ion exchange chromatographic techniques. The hemolytic activity is associated with a 107-kDa band as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and confirmed by Western blotting and immunoprecipitation. This hemolysin produces pores in membranes as demonstrated by osmotic protection studies using red blood cells and carbohydrate compounds of various molecular weights. These assays suggest a pore diameter in the order of 2 nm. Phospholipid bilayers composed of 1:1 w/w phosphotidylserine:phosphotidylethanolamine exposed to this toxin display discrete current flow events typical of transmembrane channels and consistent with the interpretation that this toxin acts by forming pores in phospholipid membranes. The linear relationship of current amplitude to holding potential when examined over the -60 to +60 mV range indicates that this pore has a constant mean single channel conductance level of 350-400 pS.
View details for Web of Science ID A1989AK17900033
View details for PubMedID 2474533
A defect in regulation of a chloride channel appears to be the molecular basis for cystic fibrosis (CF), a common lethal genetic disease. It is shown here that a chloride channel with kinetic and regulatory properties similar to those described for secretory epithelial cells is present in both T and B lymphocyte cell lines. The regulation of the channels by adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase in transformed B cells from CF patients is defective. Thus, lymphocytes may be an accessible source of CF tissue for study of this defect, for cloning of the chloride channel complex, and for diagnosis of the disease.
View details for Web of Science ID A1989T048300039
View details for PubMedID 2464852
Stimulation of human T-lymphocytes via either the surface T3-Ti antigen-major histocompatibility complex receptor complex or the T11 molecule results in clonal proliferation through a calcium-dependent mechanism. To investigate this signal transduction, plasma membrane calcium-permeable channels were characterized in T-lymphocytes by means of whole cell or single channel patch-clamp recordings. Stimulation of T-lymphocytes via either structure results in opening of an identical set of voltage-insensitive plasma membrane Ca2+-permeable channels through the action of a diffusible second messenger. Previous work with excised inside-out patches suggests that inositol 1,4,5-trisphosphate is the activating second messenger of the voltage-insensitive T-cell Ca2+-permeable channel. Since there is a significant increase in phosphoinositide turnover after stimulation via either the T3-Ti or T11 pathway, it is suggested that triggering of either structure opens a common set of channels through this mechanism. Furthermore, currents flowing through Ca2+-permeable channels are apparently autoregulated, as inward conductance is abolished by elevation of Ca2+ concentration in the bathing solution. In particular, the steady-state rise in interleukin-2 (T-cell growth factor) mRNA is dependent on the rise of [Ca2+]i resulting from ion movement across this channel.
View details for Web of Science ID A1989R820000062
View details for PubMedID 2562953
The effects of the dihydropyridine calcium channel agonist Bay K 8644 on indo-1-loaded Jurkat human leukemia T lymphocytes was assessed by flow cytometry. Bay K 8644 from 10(-9) to 10(-4) M caused a dose-dependent rise in the intracellular free Ca concentration, an effect that was not mimicked by the dihydropyridine Ca antagonist nifedipine. Single channel recordings by the extracellular patch-clamp technique indicated that Bay K 8644 activated an 8-pS, barium-permeable channel that opened as bursts of brief events. The channel appeared to be identical to the previously described voltage-insensitive, messenger-mediated, calcium-permeable channel involved in T cell activation. The predominant effect of Bay K 8644 on these channels was to increase the probability of channel reopening, apparently without a major effect on mean channel open-time. The results suggest that the dihydropyridine Ca agonist Bay K 8644 interacts with both voltage-gated and receptor-operated Ca channels and also suggest potential strategies for development of a new class of immunomodulatory drugs.
View details for Web of Science ID A1988Q219900001
View details for PubMedID 2458520