The (Ca2+, Mg2+)-ATPase activity in erythrocyte membranes from essential hypertensive patients.

The erythrocyte (Ca2+,Mg2+)-ATPase activity from 12 hypertensive and 14 normotensive subjects have been compared. No differences were found in the calcium-ATPase activity from both studied groups. When the calcium-ATPase assay was carried out in the presence of EGTA, we observed a partial stimulatory effect of the activity, but a blunted stimulation by calmodulin in both membrane preparations. When the EGTA was removed and a total concentration of calcium (100 uM) was kept constant in the incubation media, calmodulin stimulated the ATPase four fold over the non stimulated conditions in both studied groups. It is concluded that the use of EGTA buffers in the assay of the calcium-ATPase in the erythrocyte membrane of normotensive and hypertensive patients, must be used with caution, since a different enzyme sensitive to EGTA in the normotensive and the hypertensive membranes could give an erroneous interpretation of the results. This condition could partially explain the controversies in recent reports investigating the (Ca2+,Mg2+)-ATPase activity and calcium transport in different cell systems isolated from hypertensive patients.