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+/-0.92 mmol x min(-1) x l(-1)) compared with those from normotensive controls (15.22+/-0.92 mmol x min(-1) x 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.