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J. Biochem, 1976, Vol. 79, No. 6 1345-1350
© 1976 Japanese Biochemical Society

research-article

Calcium Binding and ATPase Activities of Heart Sarcolemma1

Naranjan S. DHALLA, Madhu B. ANAND and James A.C. HARROW

Pathophysiology Laboratory, Department of Physiology, Faculty of Medicine, University of Manitoba Winnipeg, Canada R3E OW3

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 50 µM and 1.25 mM Ca2+ concentrations were about 30 and 250 nmoles/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 4 mM Mg2+ or Ca2+. The Ca2+-ATPase [EC 3.6.1.3 [EC] ] activity was depressed by the presence of Mg2+ or excess ATP. Low concentrations (10 — 100 µM) 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.

1The work reported in this paper was supported by the Medical Research Council of Canada (Grant No. MT-3394).


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