The failure of endothelin to displace bound, radioactively‐labelled, calcium antagonists (PN 200/110, D888 and diltiazem)

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Abstract
The effect of endothelin, a potent vasoconstrictor polypeptide, on three types of calcium antagonist binding sites was examined, in rat cardiac membrane fragments. Endothelin 10 nM affected neither the affinity nor density of dihydropyridine binding sites. At concentrations of 10−12-10−7m, endothelin failed to displace bound (+)−[3H]-PN 200/110, (−)−[3H]-D888 and (+)−cis-[3H]-diltiazem. These results suggest that the calcium antagonist binding sites associated with L-type calcium channels are not the primary site of action of endothelin.