Kinetic study of the Ca2 + pump in erythrocytes from essential hypertensive patients

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Ca2+ pump kinetics were investigated in erythrocytes from 22 essential hypertensive patients and 20 normotensive controls (under initial-rate and steady-state conditions, using Sr2+ as a Ca2+ analogue). The mean value of the apparent dissociation constant for total internal Ca2+ (KCa) was slightly but significantly increased in the hypertensive population (73 ± 7 versus 55 ± 3 µmol/l cells, mean ± s.e.m., p=0.042 Mann—Whitney U-test). The statistical analysis showed that this was due to six essential hypertensives who exhibited a dissociation constant for Ca2+ that was higher than the upper 95% normal confidence limit (KCa=116 ± 7µmol/l cells), and abnormally high maximal pump rates {7.7 ± 0.6 versus 5.0 ± 0.2 mmol/l cells per h in normotensives, p <0.001). In addition, the apparent dissociation constant for Ca2+ was inversely correlated with plasma renin activity, although the correlation was only borderline (p =0.076). In the remaining 16 hypertensive patients, all kinetic parameters of the Ca2+ pump were within the normal range. Finally, a simultaneous study of Na + transport kinetics suggested that erythrocyte Ca2+ and Na+ transport abnormalities were independent phenomenaOur results do not support the concept that primary hypertension (as a whole entity) is associated with a ubiquitous defect in the plasma membrane Ca2+ pump. However, in some essential hypertensive patients (about 25%) the erythrocyte Ca2+ pump exhibited an apparent decreased affinity for internal Ca2 +, A similar defect in vascular smooth muscle may induce a delayed Ca2+ extrusion after the opening of Ca2 + channels, a disturbance likely to be translated into increased vascular reactivity.

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