Identification of putative calcium channels in skeletal muscle microsomes

Saturable binding sites for the labelled calcium antagonist (+/-)[3H]nimodipine were found in guinea-pig hind limb skeletal muscle homogenates. Binding sites were enriched in a microsomal pellet by differential centrifugation of the homogenate. [3H]Nimodipine binding (Kd = 1.5 +/- 0.03 nM, Bmax = 2.1 +/- 0.25 pmol/protein, at 37 degrees C) copurified (6-fold) in this fraction with [3H]ouabain binding (6.6-fold) and 125I-alpha-bungarotoxin binding (5-fold). d-cis-Diltiazem (but not 1-cis-diltiazem) stimulated (+/-) [3H]nimodipine binding (ED50 1 microM) by increasing the Bmax. Binding sites discriminated between the optical enantiomers of 1.4-dihydropyridine calcium antagonists and the optically pure enantiomers of D-600. The data confirm, with biochemical techniques, the presence of 1,4-dihydropyridine and (+/-) D-600 inhibitable calcium channels in skeletal muscle, previously found with electrophysiological techniques.