Transient activation of k+ channels by carbachol in bovine pigmented ciliary body epithelial cells. Stelling, J. W., and T. J. C. Jacob. Physiology Unit, School of Molecular & Medical Biosciences, University of Wales, PO Box 911, Cardiff, CF1 3US, UK
APStracts 3:0020C, 1996.
The action of carbachol (CCh) on isolated pigmented ciliary epithelial cells was examined using whole-cell patch clamp recording. Application of 100[mu]M CCh caused transient, occasionally oscillatory, increases in the inward and outward currents, followed by a long term decrease in both currents. Caffeine produced transient responses similar to those of CCh. The responses to CCh were blocked by the muscarinic receptor antagonist atropine, and the IP3 receptor blocker heparin (200[mu]g/ml in patch pipette). Manipulation of the internal ionic concentrations indicated that only K+ conductances were effected by CCh. Changing [Ca2+]i with the calcium ionophore ionomycin demonstrated that both the inward rectifier K+ current and the outward current exhibited Ca2+-dependence. There was no Cl- current stimulated either directly by CCh or indirectly by modulators of [Ca2+]i and any Cl- currents present arose from osmotic effects. In the short term muscarinic stimulation will activate K+ channels by causing a transient increase in [Ca2+]i. This effect only lasts for 1-5 minutes however and in the long term the conductance decreases below its original level. The effect of such a transient increase in [Ca2+]i on secretion would be complex, involving effects on gap junction communication between the pigmented and non-pigmented cell layers and the activation state of Cl- channels in the non-pigmented cells. This complexity probably accounts for the variable reports of the effects of muscarinic stimulation of the ciliary body in vivo. 

Received 25 October 1995; accepted in final form 10 January 1996.
APS Manuscript Number C648-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96