Abstract
The sarcolemmal membrane obtained from rat heart by hypotonic shock-LiBr treatment method was found to incorporate 32P from [γ- 32P] ATP in the absence and presence of cyclic AMP and protein kinase. The phosphorylated membrane showed an increase in Ca 2+ ATPase and Mg 2+ ATPase activities without any changes in Na +K + ATPase activity. The observed increase in Ca 2+ Mg 2+ ATPase activity was found to be associated with an increase in V max value of the reaction whereas K a value for Ca 2+ Mg 2+ was not altered. These results provide information concerning biochemical mechanism for increased calcium entry due to hormones which are known to elevate cyclic AMP levels in myocardium and produce a positive inotropic effect.
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