Relative sensitivities of chromaffin cell calcium channels to organic and inorganic calcium antagonists.

K-evoked 45Ca uptake into, and catecholamine release from cat adrenomedullary tissues were potently inhibited by the dihydropyridine (DHP) Ca antagonist (+)-PN 200-110 (IC50 = 0.8 nM). Verapamil and diltiazem were 2000-fold less potent and flunarizine behaved as the least potent blocker (IC50 = 2980 nM); other DHP had a full range of potencies between (+)-PN 200-110 and verapamil. The order of potencies for inorganic antagonists was Zn greater than Cd greater than La greater than Ni greater than Co greater than Mn greater than Mg. Since a great controversy exists on the sensitivity of Ca channels to various antagonists, this comprehensive study will facilitate the selection of appropriate Ca antagonists to answer fundamental questions concerning chromaffin and neural Ca channels.