Characteristics of Ca²⁺/Mg²⁺ Atpase in Heart Sarcolemma Treated with Trypsin

Abstract

Both biochemical and histochemical techniques have demonstrated the presence of an ATP- hydrolyzing enzyme in heart sarcolemma, which is activated by millimolar concentrations of various divalent cations including Ca²⁺ or Mg²⁺ (1–5). Earlier studies have revealed that the activity of this sarcolemmal Ca²⁺/Mg²⁺ ATPase was decreased by different agents, which have been shown to exert cardiodepressant effects (6–8). Furthermore, interventions, which are known to increase cardiac contractile force, were shown to increase the sarcolemmal Ca²⁺/Mg²⁺ ATPase activity (9,10). The activation of this enzyme system was found to exhibit a closed relationship with the increase in cardiac contractile force at different concentrations of Ca ²⁺ (11). The activities of sarcolemmal Ca ²⁺/Mg ²⁺ ATPase have been shown to increased under pathological situations which favour the occurrence of intracellular Ca²⁺ overload (13,14) but were depressed in other types of failing hearts (15,16). These observations support the view that Ca²⁺/Mg²⁺ ATPase may be involved in Ca²⁺-gating mechanisms and thus may play an important role in regulating the contractile force development in the cardiac muscle (11,16).