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Am J Physiol Cell Physiol 271: C203-C209, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 271, Issue 1 C203-C209, Copyright © 1996 by American Physiological Society

ARTICLES

Transient activation of K+ channels by carbachol in bovine pigmented ciliary body epithelial cells

J. W. Stelling and T. J. Jacob
Physiology Unit, School of Molecular and Medical Biosciences, University of Wales, Cardiff, United Kingdom.

The action of carbachol (CCh) on isolated pigmented ciliary epithelial cells was examined using whole cell patch-clamp recording. Application of 100 microM 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 inositol 1,4,5-trisphosphate receptor blocker heparin (200 micrograms/ml in patch pipette). Manipulation of the internal ionic concentrations indicated that only K+ conductances were affected by CCh. Changing intracellular Ca2+ concentration ([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 min, 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 nonpigmented cell layers and the activation state of Cl- channels in the nonpigmented cells. This complexity probably accounts for the variable reports of the effects of muscarinic stimulation of the ciliary body in vivo.


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