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Voltage-dependent K+ currents in smooth muscle cells from mouse gallbladder.
Jaggar J, Mawe G, Nelson MT
American Journal of Physiology-Gastrointestinal and Liver Physiology. 1998;274( 4 Pt 1):G687-93.
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Abstract
The ionic mechanisms associated with the control of gallbladder contractility are incompletely understood. One type of K+ current, the voltage-dependent K+ (KV) current, is relatively uncharacterized in gallbladder cells and may contribute to muscular excitability. The main focus of this study was therefore to determine the voltage dependence and pharmacological nature of this K+ current in isolated myocytes from mouse gallbladder, using the patch-clamp technique. Currents through Ca(2+)-activated K+ channels were minimized by buffering of intracellular Ca2+ (20 nM free Ca2+) and by inclusion of 1 mM tetraethylammonium (TEA+) in the bathing solution. With 140 mM symmetrical K+, membrane depolarization increased K+ currents, independent of driving force, as assessed by tail current analysis. Half-maximal activation of K+ currents occurred at approximately 1 mV and increased e-fold per 9 mV. Inactivation also increased on depolarization, with a midpoint of -24 mV. Single KV channels were recorded in the cell-attached configuration, exhibiting a single-channel conductance of 4.9 pS. TEA+ at 10 mM reduced KV currents by 36%. At +50 mV, 1 mM and 10 mM 4-aminopyridine inhibited currents by 18% and 35%, respectively, whereas 1 and 10 mM 3,4-diaminopyridine inhibited currents by 11% and 21%, respectively. Quinine inhibited KV currents (at +50 mV, 100 microM and 1 mM quinine inhibited current by 24% and 70%, respectively). In summary, we describe voltage-activated K+ currents from the mouse gallbladder that are likely to contribute to the control of muscular excitability.
Keyword(s)
Animals; Electric Conductivity; Electrophysiology; Female; Male; Mice; Mice, Inbred Strains; Potassium Channel Blockers; metabolism: Gallbladder; metabolism: Muscle, Smooth; pharmacology: Aminopyridines; pharmacology: Quinine; pharmacology: Tetraethylammonium; physiology: Potassium Channels