Membrane currents and cholinergic regulation of K+ current in esophageal smooth muscle cells.
The tight-seal whole cell recording technique with patch pipettes was used to study membrane currents of smooth muscle cells freshly dissociated from the esophagus of cats. Under voltage clamp with K+ in the pipette, depolarizing commands elicited an initial inward current followed by a transient outward current that peaked and then declined to reveal spontaneous outward currents (SOCs). SOCs were evident at -60 mV and more positive potentials. The reversal of SOCs at the K+ equilibrium potential and their suppression by tetraethylammonium chloride lead to the conclusion that they represent the activity of K+ channels. Acetylcholine (ACh) caused reversible contraction of these cells and had two successive effects on membrane currents, causing transient activation of K+ current followed by suppression of SOCs. Both of these effects were blocked by atropine. Consistent with these observations, in current clamp, ACh caused a transient hyperpolarization followed by depolarization. The inward current activated by depolarization was blocked by external Cd2+, consistent with the inward current being a voltage-activated calcium current. Two types of Ca2+ current could be distinguished on the basis of voltage-activation range, time course of inactivation and "run-down" during whole cell recording.
Sims
S M
SM
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
Vivaudou
M B
MB
Hillemeier
C
C
Biancani
P
P
Walsh
J V
JV
Singer
J J
JJ
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002415:Cats; D002478:Cells, Cultured; D004594:Electrophysiology / Q000379:methods; D004947:Esophagus / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000494:pharmacology*; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D015221:Potassium Channels; D002104:Cadmium; D001285:Atropine; D009116:Muscarine; D000109:Acetylcholine; D011188:Potassium