Calcium channel activation: a different type of drug action.

Publisher Website
Google Scholar
Abstract
Depolarization of NG108-15 (neuroblastoma-glioma) cells causes an increase in 45Ca2+ influx. This effect is blocked by low concentrations of dihydropyridines such as nitrendipine and by other blockers of voltage-sensitive Ca channels such as D-600 [methoxyverapamil], diltiazem and Cd2+. Two other dihydropyridines BAY K8644 [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5-carboxylate] and CGP 28392 [4-(2-difluormethoxy) phenyl-1,4,7,7-tetrahydro-2-methyl-5-oxofuropyridine-3-carboxylic acid ethyl ester], have the opposite effect. Low concentrations of these compounds enhance depolarization-induced 45Ca2+ influxes. BAY K8644 is more effective than CGP 28392. Both agents have no effect on fluxes measured under nondepolarizing conditions. The effects of BAY K8644 and CGP 28392 can be inhibited by nitrendipine, D-600, diltiazem, or Cd2+. Whereas the interaction between nitrendipine and BAY K8644 is shown to be competitive in nature, that between BAY K8644 and D-600 is shown to be noncompetitive. Dihydropyridines show a variety of effects on Ca channels, ranging from agonistic through partially agonistic to antagonistic. The results also indicate that dihydropyridines and D-600 exert their effects on Ca channels at different sites.