Modulators of calcium and potassium channels: their effects on endothelin-1 binding to cardiac membranes.
Endothelin-1 (ET-1) causes long-lasting vasoconstriction associated with a prolonged elevation of intracellular free Ca2+. Because this may be mediated through an effect on membrane ion channels, we investigated the effects of the dihydropyridine calcium channel antagonist nifedipine; two structurally distinct K+ channel openers, pinacidil and levcromakalim; and the inactive stereoisomer of levcromakalim (D-cromakalim), as well as ET-1 and ET-3, on binding of 125I-labeled endothelin-1 to rat cardiac membranes. Specific binding of 125I-ET-1 was inhibited in a concentration-dependent manner by unlabeled ET-1 (IC50 = 1.56 +/- 0.78 nM; slope = -0.49 +/- 0.10) and ET-3 (IC50 = 314 +/- 54 nM; slope = -0.34 +/- 0.11). Nifedipine, in concentrations < or = 10(-5) M, did not affect 125I-ET-1 binding. However, levcromakalim significantly inhibited 125I-ET-1 binding (maximum binding 49 4/- 9%; p = 0.04), whereas the inactive isomer, D-cromakalim, had no effect. Pinacidil also inhibited 125I-ET-1 binding, although to a lesser extent than levcromakalim (maximum binding 63 +/- 7%). These findings provide evidence for a stereospecific interaction between K(+)-channel openers and ET-1 binding in rat cardiac membranes. Because the slope of the logistic fit was substantially less than unity, and the effects of pinacidil and levcromakalim were incomplete, there may be two or more receptors for ET-1 in rat heart, only one of which is sensitive to K(+)-channel openers.
Haynes
W G
WG
Department of Medicine, University of Edinburgh, Western General Hospital, Scotland.
Waugh
C J
CJ
Dockrell
M E
ME
Olverman
H J
HJ
Williams
B C
BC
Webb
D J
DJ
D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D019806:Cromakalim; D004095:Dihydropyridines / Q000494:pharmacology; D016232:Endothelins / Q000378:metabolism*; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D011758:Pyrroles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D001578:Benzopyrans; D015220:Calcium Channels; D004095:Dihydropyridines; D016232:Endothelins; D015221:Potassium Channels; D011758:Pyrroles; D019806:Cromakalim; C038806:1,4-dihydropyridine; D009543:Nifedipine