Erythrocyte Membrane Calcium Adenosine 5′-Triphosphatase Activity in the Spontaneously Hypertensive Rat

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Abstract
Ca2+-Mg2+-ATPase activity was studied simultaneously in calmodulin-deficient erythrocyte ghost membranes and inside-out vesicles (IOVs) from 12-week-old female spontaneously Hypertensive rats (SHR) and their matched controls: [Wistar-Kyoto normotensive rats (WKY)], and in detergent extracts of ghost membranes. Both ATP-dependent Ca2+ uptake by IOVs and Ca2+-dependent ATP hydrolysis activity of ghost membranes were reduced significantly in the SHR compared with WKY, when either the calmodulin-independent or clamodulin-stimulated activities were compared. The ratios between Ca2+ uptake and ATP hydrolysis activities in the SHR remained approximately 1.0, showing a proportional reduction in both activities. No difference in affinity for calmodulin was observed between SHR and WKY. No significant difference in Ca2+-dependent ATP hydrolysis activity was observed between SHR and WKY after detergent solubilization of erythrocyte ghost membranes. These results suggest that the number of Ca2+-Mg2+-ATPase units are similar in SHR and WKY and that the reduced activity in the intact SHR membrane is due to altered membrane environment.