Dihydropyridine-sensitive Ca2+ channels: molecular properties of interaction with Ca2+ channel blockers, purification, subunit structure, and differentiation.

[3H]Desmethoxyverapamil, (S/-)[3H]bepridil, and d-cis-[3H]diltiazem bind to skeletal muscle transverse-tubule (T-tubule) membranes with affinity constants in the range of 2-50 nM and with Bmax values of the order of 50-80 pmol/mg of protein. These drugs are mutually competitive and modulate allosterically the 1,4-dihydropyridine binding. The molecular size of the native [3H]nitrendipine receptor of T-tubule membranes has been determined using the radiation inactivation technique. The [3H]nitrendipine receptor was found to have a Mr of 210,000 +/- 20,000. Photoaffinity labelling using (+)[3H]PN 200-110 indicates the presence in the dihydropyridine receptor of a polypeptide (or polypeptides) of Mr 170,000 +/- 5,000. The 3-[(3-cholamidopropyl)-dimethylammonio]-1 propane sulfonate (CHAPS) solubilization of the T-tubule membranes preserved the binding properties of the different drugs to the calcium channel. The dihydropyridine-sensitive calcium channel has been substantially purified by a combination of ion exchange chromatography, lectin affinity chromatography, and gel filtration. The purified material contained polypeptides of apparent molecular weights of 142,000, 32,000, and 33,000, which copurified with (+)[3H]PN 200-110 binding activity. Two stages in which there is an increased binding of [3H]nitrendipine have been observed during chick myogenesis in ovo. The first one occurs during embryonic life and has the same properties as in the in vitro development. The second stage occurs near hatching and corresponds to a large increase in the number of nitrendipine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)