Neutrophil intracellular pH and Na+/H+ exchanger activity in pre-eclampsia

Elevated Na(+)/H(+) exchanger activity and intracellular acidosis have previously been demonstrated in white blood cells isolated from women who have suffered from a pre-eclamptic pregnancy. The mechanisms underlying this abnormality and the implications in pre-eclamptic pregnancies are, at present, unclear. In this study, we used neutrophils from third trimester pre-eclamptic patients and third trimester normotensive pregnant controls to determine Na(+)/H(+) exchanger isoform-1 (NHE-1) activity and intracellular pH. This was performed using a well-validated technique involving flurometry and a pH sensitive dye, 2,7'Bis-(carboxyethyl) 5.6 carboxyfluorescein acetomethyl ester (BCECF-AM). Time course experiments were performed to assess the contribution of plasma factors to intracellular pH measurements. Plasma digoxin-like factor (DLF) was assessed in both patients and normotensive controls. Neutrophil intracellular pH was significantly lower in the pre-eclamptic patients (7.15 +/- 0.050) compared with the normotensive pregnant controls (7.36 +/- 0.027; P<.001). NHE-1 activity (in mmol/L/min) was significantly higher in the pre-eclamptics (32.4 +/- 1.9) compared with the normotensive neutrophils (27.1 +/- 1.6; P =.038). Times course experiments showed that mean pre-eclamptic intracellular pH increased from 7.11 +/- 0.049 to 7.25 +/- 0.043 after 2 hours of incubation. DLF, measured as amount of inorganic phosphate liberated from adenosine triphosphate (ATP), was significantly lower when plasma from the pre-eclamptic patients was incubated with the enzyme compared with plasma from the normotensive pregnant women (54.9 +/- 2.6 nmol/mL plasma v 63.91 +/- 1.7 nmol/mL plasma, n = 6, P =.018 unpaired Student's t test). The results suggest that elevated NHE-1 activity and intracellular acidosis are intermediate phenotypes in women who have pre-eclampsia. Intracellular pH may have been affected by plasma as shown in the time course experiments. DLF, an inhibitor of Na(+)/K(+)ATPase, may contribute to this intracellular acidosis in pre-eclamptic neutrophils.