Previous studies have demonstrated a raised Na+ content in leucocytes isolated from women with pre-eclampsia. Increased Na+/H+ exchanger activity is one membrane transport abnormality that may contribute to this phenomenon and may be implicated in the abnormal volume homoeostasis and hypertension associated with the disease. Increased Na+/H+ exchanger activity has been documented in nucleated white blood cells from both pre-eclamptic and post-partum pre-eclamptic women, and may suggest the importance of genetic influences on exchanger activity. In the present study, we used lymphoblasts from women with pre-eclampsia and from age- and gestation-matched normotensive pregnant controls to determine Na+/H+ exchanger activity and intracellular resting pH using fluorimetry and the pH-sensitive dye BCECF-AM [bis(carboxyethyl)carboxyfluorescein acetoxymethyl ester]. Determination of Na+/H+ exchanger protein abundance was performed by Western blotting. Intracellular pH was not significantly different in cells from pre-eclamptic women compared with those from normotensive controls. Na+/H+ exchanger activity was measured when the intracellular pH was clamped at 6.0, and was found to be significantly higher in cells from pre-eclamptic women (20.77±0.92mmol·min-1·l-1) compared with those from normotensive controls (15.22±0.92mmol·min-1·l-1; P = 0.001). Na+/H+ exchanger protein abundance was established to be similar in the two subject groups, suggesting that the turnover number for the Na+/H+ exchanger is increased in the women with pre-eclampsia. These changes in Na+/H+ exchanger activity indicate the importance of genetic factors in determining this particular phenotype, since in this cell culture model of pre-eclampsia it is likely that environmental or hormonal influences present in vivo would have declined. Overactivity of the Na+/H+ exchanger may contribute to the raised intracellular Na+ concentration reported previously in white blood cells from women with pre-eclampsia.

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