Transient outward current in the opossum esophageal circular muscle. Akbarali, Hamid I., Noboru Hatakeyama, Qiang Wang, and Raj K. Goyal. Center for Swallowing and Motility Disorders, Gastroenterology Division, Beth Israel Hospital and Harvard Medical School, 330 Brookline Ave, Boston MA 02215
APStracts 2:0011G, 1995.
The whole-cell patch clamp technique was used to record a transient outward K+ current (ITO) from single smooth muscle cells isolated from opossum esophageal circular muscle. The threshold for its activation was -50 mV from holding potentials negative to -70 mV. The current peaked within 10 msec and decayed completely in 200 msec between test depolarization of -40 mV and -10 mV. ITO was recorded at room temperature in the presence of 5 mM internal EGTA . Both activation and inactivation kinetics of ITO were markedly changed when recordings were made at higher temperatures (32 oC) . 4 -Aminopyridine (3 mM) abolished the fast component of the outward current. Tetraethylammonium ion (1-30 mM) reduced the sustained component but did not affect ITO. In the presence of TEA and nifedipine, the voltage dependence of the steady-state inactivation data were well fitted by a Boltzmann distribution with a half -inactivation potential of -57 mV. The half-inactivation potential was shifted to more positive potential in the presence of Cd2+ (-35 mV). The steady-state inactivation and activation data overlap between -50 mV and -30 mV suggesting the presence of a 'window' current in this potential range. In current clamp mode, 4AP depolarized single esophageal cells by about 8 mV and shifted the upstroke of the action potential to the left. These results indicate that in the esophageal circular muscle, ITO is involved in the resting membrane potential and modulation of the onset of action potential. 

Received 3 October 1994; accepted in final form 16 January 1995.
APS Manuscript Number G392-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.