Gating and blocking of calcium channels by dihydropyridines in the pancreatic B-cell

The organic calcium-antagonist nifedipine inhibits glucose-stimulated 45Ca net uptake and insulin release by rat pancreatic islets. However, the chemically related dihydropyridine derivative BAY K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5- carboxylate) enhances 45Ca net uptake and insulin release and protects the B-cell against the inhibitory action of nifedipine. It is proposed that a regulatory site exists in or near the calcium channels, in the B-cell plasma membrane, and that occupation of this site by selected dihydropyridines may either facilitate or inhibit Ca2+ influx into the B-cell.