Characteristics and physiological role of the calcium-activated chloride conductance in smooth muscle. Large, William A., and Qiang Wang. Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London SW17 0RE, UK; Department of Animal Biology, Laboratory of Pharmacology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104
APStracts 3:0004C, 1996.
In this review we discuss the properties of the calcium-activated chloride current (ICl(Ca)) recorded in isolated smooth muscle cells with electrophysiological techniques and speculate on the possible physiological role(s) of ICl(Ca) in smooth muscle function. In particular we concentrate on 1) the Ca-dependence of ICl(Ca), 2) the mechanisms that link pharmacological receptor stimulation on the cell surface membrane to activation of ICl(Ca), 3) the biophysical properties of ICl(Ca), and 4) the pharmacology of ICl(Ca). It is evident that a diverse array of pharmacological agonists can evoke ICl(Ca) in many types of smooth muscle and it seems that the well -established G-protein-phosphoinositide metabolism (IP3) - intracellular calcium store pathway couples the receptor to the membrane channels. Also the results indicate that the biophysical and pharmacological properties of ICl(Ca) are not only similar in the various smooth muscle types studied so far but, possibly, also to ICl(Ca) in non-smooth muscle tissue. Evidence will be presented that the calcium-activated chloride channel exists in two states, open and closed, with a relatively long mean open time and that some of the agents that inhibit ICl(Ca) interact directly with the open channel. It is suggested that the most likely role of ICl(Ca) in smooth muscle is to produce membrane depolarization and contraction to neurotransmitters and local mediators. 

Received 17 November 1995; accepted in final form 1 December
1995.
APS Manuscript Number C734-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96