Nitrendipine and isoproterenol induce phosphorylation of a 42,000 dalton protein that co-migrates with the affinity labeled calcium channel regulatory subunit

Slow inward calcium channels in canine cardiac membranes were affinity labeled with the calcium channel analogue, [³H]o-NCS [2,6 dimethyl-3,5-dicarbomethoxy-4-(2-isothiocyanatophenyl)-1,4-dihydropyridine], in the presence and absence of cold o-NCS or nicardipine. A major specifically labeled peak was identified with M_r 42,000 on NaDodSO₄ polyacrylamide gels. In parallel experiments the effects of the calcium channel antagonist, nitrendipine and a variety of other chemical mediators were tested for their ability to stimulate protein phosphorylation in cardiac membranes. These data demonstrate that both nitrendipine and isoproterenol induce the phosphorylation of a 42,000 dalton protein via a kinase endogenous to the cardiac membranes and that the effects of isoproterenol are attenuated by carbachol.