title: Calcium and potassium currents in canine gastric smooth muscle cells.
abstract: Membrane ionic currents were recorded in single smooth muscle cells dissociated from circular muscle of dog stomach (corpus region). When studied under voltage clamp with K+ in the patch electrode, depolarization to potentials more positive than -40 mV, from a holding potential of -70 or -80 mV, evoked transient inward current followed by outward current. Evidence that the outward current was due to K+ came from analysis of deactivation tail currents, which reversed direction close to the K+ equilibrium potential. In addition, the outward current was reduced by tetraethylammonium (TEA, 1-5 mM) applied to the external surface of cells. The Ca(2+)-channel blocker Cd2+ blocked the inward current and also reduced outward current, suggesting Ca(2+)-activated K+ current contributed to the outward current. The voltage-activated inward current was studied in isolation with Cs+ and TEA in the recording electrode to block K+ current. In standard bathing solution containing 2.5 mM Ca2+, the inward current activated between -50 and -40 mV, with peak inward current at +10 mV. The depolarization-activated inward current was blocked by nifedipine and enhanced by BAY K 8644, providing evidence that it was Ca2+ current. The Ca2+ current showed transient and sustained components, both of which showed similar voltage activation and inactivation ranges. The half-inactivation potential was approximately -37 mV. These results provide evidence that smooth muscle cells from the canine gastric corpus possess K+ and Ca2+ channels. Based on the voltage dependence of activation and inactivation and sensitivity to dihydropyridines, L-type Ca2+ channels predominate in canine gastric corpus smooth muscle.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Sims
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004285:Dogs; D004594:Electrophysiology; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D013270:Stomach / Q000166:cytology / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D011188:Potassium; D002118:Calcium