A NONSELECTIVE CATION CHANNEL IN RABBIT CORNEAL ENDOTHELIUM ACTIVATED BY INTERNAL CALCIUM AND INHIBITED BY INTERNAL ATP

The apical membrane of the rabbit corneal endothelium contains a cation selective channel of 21·7 ± 0·4 pS conductance which is activated by internal Ca2+ and inhibited by internal ATP. Patch clamp studies show the channel to be quite selective for cations over anions but not to select between Na+ and K+. In excised patches in the inside-out configuration, the open probability increases when the internal Ca2+ is raised above 10-4 m. ATP decreases the open probability when its internal concentration exceeds 10 μm. At 1 mm ATP, no channel openings are ever seen. AMP and ADP also inhibit at least as well as does ATP. One μm AMP-PNP, a non-hydrolyzable ATP, also inhibits gating and so phosphorylation by a PO4-3 cleaved from ATP is not the mechanism of ATP inhibition. The channel is apparently impermeable to divalent ions since neither Ba2+ nor Ca2+ carry any detectable current. Quinidine produces a flickery, weakly voltage dependent blockade when applied to the channel's cytoplasmic surface. Both Ca2+ and ATP work at concentrations not expected to occur inside healthy cells. It is presently uncertain if this is a physiologically important channel in these cells. © 1990.