Comparison of (Ca2+-Mg2+)-ATPase and Ca2+-ATPase in rat cardiac sarcolemma.

The calcium dependency of the Ca2+-pump ATPase of rat cardiac sarcolemma was investigated in the presence and absence of EGTA and EDTA in combination with two free Mg2+-ion concentrations. The results showed: that Mg2+-ions are not essential for the turnover of the Ca2+-pump ATPase; that the Ca2+-affinity is regulated by the concentration of the calcium-chelator complex present in the medium; that (Ca2+-Mg2+)-ATPase and Ca2+-ATPase are probably expressions of the same Ca2+-pump ATPase in the plasma membrane of the cell.