CA2-INDUCED ALTERATIONS IN THE ACTIVITY OF MEMBRANE (CA2+-MG2+)-ATPASE OF HUMAN AND RAT ERYTHROCYTES()

Effect of intraerythrocyte Ca2+ elevation on human and rat erythrocyte membrane (Ca2+Mg2+)-ATPase along with that of incubation of the eryth rocyte ghosts in their own hemolysates enriched With Ca2+ has been stu died. While the membrane (Ca2+-Mg2+)-ATPase levels of Ca2+-loaded huma n erythrocytes showed an initial increase and subsequent decline, memb ranes incubated in their own hemolysate showed a consistent decrease i n the enzyme activity. Calmodulin sensitivity was by the preparations in contrast to the earlier observations made with washed erythrocyte m embranes. Similar changes in (Ca2+-Mg+)-ATPase activity but of greater magnitude were observed in response to Ca2+ in the calpain-rich rat e rythrocytes. Considerable crosslinking and proteolysis was observed in case of human and rat erythrocytes exposed to high Ca2+ concentration s. The Ca2+-activable transglutaminase, however, did not play any role in the activation of the (Ca2+-Mg2+)-ATPase.