A calmodulin dependent protein kinase activity associated with rabbit heart sarcolemma

Abstract

Sarcolemmal vesicles prepared from rabbit heart muscle by differential and discontinuous sucrose density gradient centrifugation, exhibited high marker enzyme activities: Na⁺ + K⁺ ATPase 22 µMol Pi × mg⁻¹ × h⁻¹. Adenylate cyclase 500 pmole CAMP × mg⁻¹ × min⁻¹, calcium antagonist receptors 0.7 pmoles × mg⁻¹. Calmodulin in the presence of calcium and γ-ATP³² stimulated rapidly and specifically the ³²P incorporation into two membrane proteins of 54 and 44 kDa. Calmodulin stimulated the phosphorylation of the 44 kDa to a greater extent (17.9 pmol ³²P × mg⁻¹ protein) than the 54 kDa protein (1.3 pmoles ³²P x mg⁻¹ protein). Removal of endogenous calmodulin from the membrane by EGTA extraction resulted in a 2.5 fold increase in calmodulin dependent ³²P incorporation into the two proteins in the presence of exogenous calmodulin. It is suggested that the calmodulin dependent protein kinase activity in heart sarcolemma may mediate the effects of calmodulin in the regulation of Ca²⁺ transport across the membrane.