title: Inwardly rectifying K(+) channels in esophageal smooth muscle.
abstract: The whole cell patch-clamp technique was used to investigate whether there were inwardly rectifying K(+) (K(ir)) channels in the longitudinal muscle of cat esophagus. Inward currents were observable on membrane hyperpolarization negative to the K(+) equilibrium potential (E(k)) in freshly isolated esophageal longitudinal muscle cells. The current-voltage relationship exhibited strong inward rectification with a reversal potential (E(rev)) of -76.5 mV. Elevation of external K(+) increased the inward current amplitude and positively shifted its E(rev) after the E(k), suggesting that potassium ions carry this current. External Ba(2+) and Cs(+) inhibited this inward current, with hyperpolarization remarkably increasing the inhibition. The IC(50) for Ba(2+) and Cs(+) at -60 mV was 2.9 and 1.6 mM, respectively. Furthermore, external Ba(2+) of 10 microM moderately depolarized the resting membrane potential of the longitudinal muscle cells by 6.3 mV while inhibiting the inward rectification. We conclude that K(ir) channels are present in the longitudinal muscle of cat esophagus, where they contribute to its resting membrane potential.
authors.affiliation: Departments of Medicine and Physiology, University of Toronto, and Playfair Neuroscience Unit, Toronto Western Hospital, Toronto, Ontario, Canada M5T 2S8.
authors.forename: J
authors.initials: J
authors.lastname: Ji
authors.forename: A M
authors.initials: AM
authors.lastname: Salapatek
authors.forename: N E
authors.initials: NE
authors.lastname: Diamant
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002415:Cats; D002586:Cesium / Q000494:pharmacology; D004947:Esophagus / Q000737:chemistry / Q000502:physiology*; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000737:chemistry / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D012964:Sodium / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D002586:Cesium; D001464:Barium; D012964:Sodium; D008274:Magnesium; D011188:Potassium