The bovine cardiac receptor for calcium channel blockers is a 195‐kDa protein

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Abstract
The cardiac receptor for calcium channel blockers was purified from bovine microsomal membranes which contained 235 .+-. 33 fmol nimodipine-binding sites/mg protein (mean .+-. SEM of nine preparations). To identify the receptor during the purification 20% of its binding sites were prelabeled with (+)[3H]PN200-110. The receptor was solubilized with 0.6% digitonin and was purified to a specific density of 157 pmol/using a combination of ion-exchange, wheat-germ-agglutinin-Sepharose chromatography and sucrose density gradient centrifugation. In the last sucrose gradient bound (+)[3H]PN200-110 comigrated with a 195-kDa protein. (.+-.)[3H]Azidopine and [3H]ludopamil, the photoaffinity ligands for the dihydropyridine and phenylakylamine-binding site of the calcium channel, were incorporated specifically into the 195-kDa protein. These data indicate that the bovine cardiac receptor for calcium channel blockers is a 195-kDa protein. Its molecular mass suggests that the bovine cardiac receptor differs considerably from the rabbit skeletal muscle receptor protein for calcium channel blockers.

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