AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 5 794-G802, Copyright © 1990 by American Physiological Society

ARTICLES

Membrane currents and cholinergic regulation of K+ current in esophageal smooth muscle cells

S. M. Sims, M. B. Vivaudou, C. Hillemeier, P. Biancani, J. V. Walsh Jr and J. J. Singer
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.

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.

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