Potentiating effect of calmodulin and catalytic subunit of cyclic AMP-dependent protein kinase on ATP-dependent Ca2+-transport by cardiac sarcolemma

AbstractHighly purified sarcolemmal membranes were prepared from pig heart homogenates by differential and density gradient centrifugations. The membrane fragments exhibit ATP-dependent Ca2+-transport and Na+/Ca2+-exchange activities. ATP-dependent Ca2+-transport (KCa2+0.5 = 0.3 μM; Vmax = 4.6 nmol Ca2+•mg protein−1 •min−1)_is not stimulated by oxalate. Ca2+-uptake is also not supported by p-nitrophenylphosphate. Preincubation of sarcolemma with MgATP, calmodulin and catalytic subunit of cyclic AMP-dependent protein kinase stimulates active Ca2+-transport 1.8-fold. The effects of calmodulin and catalytic subunit are potentiating rather than additive. A large portion of the Ca2+ additionally accumulated after prephosphorylation of membranes is exchangable for Na+ via the Na+/Ca2+-exchange system