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The (Ca2+, Mg2+)-ATPase activity in erythrocyte membranes from essential hypertensive patients
A Gutiérrez1, R Ariza, A C Frati-Munari
1Departamento de Medicina Interna, Hospital de Especialidades, Centro Médico La Raza, IMSS, México, D.F.
Insights
Erythrocyte calcium-ATPase activity showed no baseline differences between hypertensive and normotensive individuals. Caution is advised when using EGTA buffers in assays due to potential misinterpretation of results in hypertension research.
Area of Science:
- Biochemistry
- Cardiovascular Physiology
- Cellular Biology
Background:
- Erythrocyte (Ca2+,Mg2+)-ATPase is crucial for calcium homeostasis.
- Previous studies on erythrocyte ATPase in hypertension have yielded conflicting results.
Purpose of the Study:
- To compare erythrocyte (Ca2+,Mg2+)-ATPase activity between hypertensive and normotensive subjects.
- To investigate the influence of EGTA and calmodulin on ATPase activity in both groups.
Main Methods:
- Assay of erythrocyte (Ca2+,Mg2+)-ATPase activity.
- Comparison between 12 hypertensive and 14 normotensive subjects.
- Evaluation of EGTA and calmodulin effects on enzyme activity.
Main Results:
- No significant differences in basal calcium-ATPase activity were observed between groups.
- EGTA showed a partial stimulatory effect, with blunted calmodulin stimulation in both groups.
- Calmodulin significantly stimulated ATPase activity (four-fold) when EGTA was absent and calcium was 100 uM.
Conclusions:
- Use of EGTA buffers in erythrocyte calcium-ATPase assays requires caution, especially when comparing hypertensive and normotensive patients.
- EGTA-sensitive enzymes may lead to erroneous interpretations, potentially explaining discrepancies in hypertension research.
- Findings highlight the importance of assay conditions for understanding calcium transport in hypertension.
Abstract:
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.