Caffeine- and carbachol-induced chloride and cation currents in
single opossum esophageal circular muscle cells.
Wang, Q., H. I. Akbarali, N. Hatakeyama, and R. K. Goyal.
Center for Swallowing and Motility Disorders, Harvard-Thorndike Lab
and Charles, A Dana Research Institute, Gastroenterology Division,
Department of Medicine, Beth Israel Hospital, Harvard Medical School,
330 Brookline Avenue, Boston, MA 02115
APStracts 3:0214C, 1996.
Chloride and cation currents may play important role in esophageal
smooth muscle membrane potential changes and contraction. We studied
calcium release-activated cell-shortening and membrane currents in
single cells freshly dispersed from the circular muscle of the
opossum esophagus using the standard patch clamp whole-cell recording
method. Caffeine (10-20 Mm) and Carbachol (CCh, 10-100 _M) shortened
the single smooth muscle cells by releasing intracellular calcium. At
a holding potential of 0 mV, spontaneous transient outward currents
(STOCs, representing spontaneous Ca-activated potassium currents)
were recorded; Caffeine, Cch or ionomycin evoked large outward
currents (up to 1650 Pa) and subsequently abolished STOCs. At a
holding potential of -50 Mv in K-containing solutions, an outward
current in response to the agonists was observed; in some cells the
outward current followed an inward current. In K-free solutions the
agonists induced only an inward current whose reversal potential (Er)
was shifted by alteration of the anion gradient, but not by that of
the cation. With a low-Cl pipette solution (Cl substituted by
glucuronate or glutamate), the inward currents were dependent mainly
on the external cation gradient. This cation channel was permeable to
Ba2+. Inclusion of 10 Mm EGTA in the pipette solution, abolished all
these currents. These data suggest that in the opossum esophageal
circular muscle: (1) Ca2+ released from the intracellular stores by
caffeine and CCh is sufficient to induce single smooth muscle cell
contraction; (2) the caffeine-, CCh-and ionomycin-induced membrane
currents consist of Ca2+ - activated IKCa, I ClCa and ICat
conductances.
Received 29 June 1995; accepted in final form 28 May 1996.
APS Manuscript Number C390-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996