Diversity of K+ channels in circular smooth muscle of opossum lower esophageal sphincter.
We previously demonstrated that a balance of K+ and Ca2+-activated Cl- channel activity maintained the basal tone of circular smooth muscle of opossum lower esophageal sphincter (LES). In the current studies, the contribution of major K+ channels to the LES basal tone was investigated in circular smooth muscle of opossum LES in vitro. K+ channel activity was recorded in dispersed single cells at room temperature using patch-clamp recordings. Whole-cell patch-clamp recordings displayed an outward current beginning to activate at -60 mV by step test pulses lasting 400 ms (-120 mV to +100 mV) with increments of 20 mV from holding potential of -80 mV ([K+]I = 150 mM, [K+]o = 2.5 mM). However, no inward rectification was observed. The outward current peaked within 50 ms and showed little or no inactivation. It was significantly decreased by bath application of nifedipine, tetraethylammonium (TEA), 4-aminopyridine (4-AP), and iberiotoxin (IBTN). Further combination of TEA with 4-AP, nifedipine with 4-AP, and IBTN with TEA, or vice versa, blocked more than 90% of the outward current. Ca2+-sensitive single channels were recorded at asymetrical K+ gradients in cell-attached patch-clamp configurations (100.8+/-3.2 pS, n = 8). Open probability of the single channels recorded in inside-out patch-clamp configurations were greatly decreased by bath application of IBTN (100 nM) (Vh = -14.4+/-4.8 mV in control vs. 27.3+/-0.1 mV, n = 3, P < 0.05). These data suggest that large conductance Ca2+-activated K+ and delayed rectifier K+ channels contribute to the membrane potential, and thereby regulate the basal tone of opossum LES circular smooth muscle.
Zhang
Y
Y
Department of Medicine and Physiology, Queen's University, Kingston, ON, Canada.
Paterson
W G
WG
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004943:Esophagogastric Junction / Q000187:drug effects / Q000502:physiology*; D005260:Female; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009893:Opossums / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D002118:Calcium