Calcium Binding and ATPase Activities of Heart Sarcolemma

抄録

Rat heart sarcolemma prepared by the hypotonic shock-LiBr treatment method was found to bind calcium by a concentration-dependent and saturable process. The calcium binding values at 50μM and 1.25mM Ca²⁺ concentrations were about 30 and 250nmoles/mg protein, respectively. Both Mg²⁺ and ATP inhibited calcium binding and no evidence for energy-linked calcium binding with sarcolemma was found. On the other hand, maximal ATP hydrolysis by heart sarcolemma was seen at 4mM Mg²⁺ or Ca²⁺. The Ca²⁺-ATPase [EC 3.6.1.3] activity was depressed by the presence of Mg²⁺ or excess ATP. Low concentrations (10-100μM) of Ca²⁺ failed to stimulate ATP hydrolysis in the presence of various concentrations of Mg-ATP. These results indicate the absence of a “calcium pump” mechanism in the heart sarcolemmal membrane preparation employed in this study.