Identification of putative calcium channels in skeletal muscle microsomes

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Abstract
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 (K d = 1.5±0.03 nM, B max = 2.1 ± 0.25 pmol/protein, at 37°C) copurified (6‐fold) in this fraction with [3H]ouabain binding (6.6‐fold) and 125I‐α‐bungarotoxin binding (5‐fold). d‐cis‐Diltiazem (but not 1‐cis‐diltiazem) stimulated (±) [3H]nimodipine binding (ED 50 1 μM) by increasing the B max. 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.