A non-selective 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 microM. At 1 mM ATP, no channel openings are ever seen. AMP and ADP also inhibit at least as well as does ATP. One microM 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.
Department of Physiology, Mayo Foundation, Rochester, MN 55905.
J L
JL
Rae
J
J
Dewey
K
K
Cooper
P
P
Gates
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D004728:Endothelium, Corneal / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D011802:Quinidine / Q000494:pharmacology; D011817:Rabbits
D007473:Ion Channels; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D011802:Quinidine; D002118:Calcium