Differential labelling of putative skeletal muscle calcium channels by [3H]-nifedipine, [3H]-nitrendipine, [3H]-nimodipine and [3H]-PN 200 110

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Abstract
Summary Four 1,4-dihydropyridine calcium channel blockers [3H]-nifedipine, [3H]-nitrendipine, [3H]-nimodipine and [3H]-PN 200 110 (Isopropyl 4-(2,1,3,benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-methoxy-carbonylpyridine-3-carboxylate) were employed to label putative calcium channels in guinea-pig hind limb skeletal muscle membranes. The four radioligands differed with respect to the number of sites (B max) which were labelled. The following rank order of B max values was found: PN 200 110 > nimodipine = nitrendipine > nifedipine. d-cis-Diltiazem caused an increase in the density of high-affinity binding sites for all four calcium channel blockers. The relative stimulation was smallest for PN 200 110. It is suggested that 1,4-dihydropyridines exhibit different efficacies for induction of a channel state with high affinity for these drugs.