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J A Tabcharani

Publications and source records attributed to J A Tabcharani.

23 records · Page 2Linked to original sources
PubMed1990

Inhibition of an outwardly rectifying anion channel by HEPES and related buffers.

The effect of pH buffers and related compounds on the conductance of an outwardly rectifying anion channel has been studied using the patch-clamp technique. Single-channel current-voltage relationships were determined in solutions buffered by trace amounts of bicarbonate and in solutions containing N-substituted taurines (HEPES, MES, BES, TES) and glycines (glycylglycine, bicine and tricine), Tris and bis-Tris at millimolar concentrations. HEPES (pK alpha = 7.55) reduced the conductance of the channel when present on either side of the membrane. Significant inhibition was observed with 0.6 mM HEPES on the cytoplasmic side (HEPESi) and this effect increased with [HEPESi] so that conductance at the reversal potential was diminished approximately 25% with 10 mM HEPEsi and approximately 70% at very high [HEPESi]. HEPESi block was relieved by applying positive voltage but positive currents were not consistent with a Woodhull-type blocking scheme in that calculated dissociation constants and electrical distances depended on HEPES concentration. Results obtained by varying total HEPESi concentration at constant [HEPES-] and vice versa suggest both the anionic and zwitterionic (protonated) forms of HEPES inhibit. Structure-activity studies with related compounds indicate the sulfonate group and heterocyclic aliphatic groups are both required for inhibition from the cytoplasmic side. TES (pK alpha = 7.54), substituted glycine buffers (pK alpha = 8.1-8.4) and bis-Tris (pK alpha = 6.46) had no measurable effect on conductance and appear suitable for use with this channel.

Buffers↗
PubMed1990

Transformed sweat gland and nasal epithelial cell lines from control and cystic fibrosis individuals.

We undertook to extend the in vitro lifespan of epithelial cell cultures useful for the study of the cellular defect underlying cystic fibrosis (CF). Primary cultures from sweat glands of four CF and four non-CF and from nasal polyps of one non-CF and two CF individuals were transformed using a chimaeric virus, Ad5/SV40 1613 ori-. The extended lifespans ranged from 20 to more than 250 population doublings beyond that of the primary cultures. Despite some degree of aneuploidy (as assayed by total cellular DNA content) all samples tested retained at least one copy of the region of chromosome 7 containing the CF gene (as assayed by probing with flanking DNA markers). Epithelial characteristics, including an epithelioid morphology, tight junctions and desmosomes, apical microvilli, keratin networks, and dome formation were positive in the majority of cells examined, although variably expressed. All cells tested demonstrated outwardly rectifying chloride channels by patch clamp, with some from non-CF cells responsive to the catalytic subunit of cyclic AMP-dependent protein kinase. The cells were used for DNA transfection assays with selectable marker genes in appropriate vectors, in order to develop methodology for assaying the function of the CF gene product and the effects of mutations.

Cell Division↗
PubMed1989

Ca2+-activated K+ channel in rat pancreatic islet B cells: permeation, gating and blockade by cations.

Activation of Ca2+-dependent K+ conductance has long been postulated to contribute to the cyclical pauses in glucose-induced electrical activity of pancreatic islet B cells. Here we have examined the gating, permeation and blockade by cations of a large-conductance, Ca2+-activated K+ channel in these cells. This channel shares many features with BK (or maxi-K+) Ca2+-activated K+ channels in other cells. (1) Its 'permeability' selectivity sequence is PT1+: PK+: PRb+: PNH4+: PNa+, Li+, Cs+ = 1.3:1.0:0.5:0.17: less than 0.05. Permeant, as well as impermeant, cations reduce channel conductance. (2) Its conductance saturates at 325-350 pS with bath KCl greater than 400 mM (144 mM KCl pipette). (3) It shows asymmetric blockade by tetraethylammonium ion (TEA) and Na+. (4) It is sensitive to Ca2+i over the range 5 nM-100 microM; over the range 50-200 nM, channel activity varies as [Ca2+ free]1-2. (5) It is sensitive to internal pH over the range 6.85-7.35, but the decrease in channel activity seen with reduced pHi may be partially compensated by the increase in free Ca2+ concentration which occurs on acidification of buffered Ca2+/EGTA solutions.

Animals↗
PubMed1989

Bicarbonate permeability of the outwardly rectifying anion channel.

Single anion-selective channels have been studied in cultured human epithelial cells using the patch-clamp technique. Three cell types were used as models for different anion transport systems: (i) PANC-1, a cell line derived from the pancreatic duct, (ii) T84, a Cl-secreting colonic cell line, and (iii) primary cultures of sweat duct epithelium. Outwardly rectifying anion-selective channels were observed in all three preparations and were indistinguishable with respect to conductance, selectivity and gating. Striking similarities between HCO3- and Cl-secreting epithelia, and the high density of outward rectifiers in pancreatic cells prompted us to study HCO3 permeation through this channel. HCO3 permeability was significant when channels were bathed in symmetrical 150 mM HCO3 solutions, Cl-HCO3 mixtures, and under bi-ionic conditions with outwardly and inwardly directed HCO3 gradients. Permeability ratios (PHCO3/PCl) estimated from bi-ionic reversal potentials ranged from 0.50 to 0.64, although conductance ratios greater than 1.2 were observed with high extracellular pH. Chloride did not inhibit HCO3 permeation noticeably but rather had a small stimulatory effect when present on the opposite side of the membrane. The prevalence of outward rectifiers in PANC-1 and their permeability to bicarbonate suggests the channel may have a dual role in HCO3 secretion; to allow Cl recycling at the apical membrane and to mediate some of the HCO3 flux. Defective modulation of this channel in cystic fibrosis might provide a common basis for dysfunction in epithelia having very different anion transport properties (e.g., HCO3 secretion, Cl secretion and Cl absorption.

Bicarbonates↗