ENHANCED NA+-H+ EXCHANGER ACTIVITY AND NHE-1 MESSENGER-RNA EXPRESSION IN LYMPHOCYTES FROM PATIENTS WITH ESSENTIAL-HYPERTENSION

It has been demonstrated that the activity of the sodium-proton exchanger (NHE-1 isoform) is increased in lymphocytes and other blood cells from patients with essential hypertension. In the present study, we investigated whether an increased level of NHE-1-specific mRNA in lymphocytes from patients with essential hypertension would explain the enhanced transport activity. Twenty-two hypertensive patients and 21 normotensive subjects were studied. Basal cytosolic pH was measured by the pH-sensitive fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Maximal sodium-proton exchange activity was determined by acidifying cell pH and measuring the initial rate of the net sodium-dependent proton efflux driven by an outward proton gradient. The transcript level of NHE-1 was measured by reverse transcription-polymerase chain reaction in comparison with a constitutively expressed reference gene (beta-actin). Intracellular pH was lower in hypertensive patients than normotensive subjects (7.34+/-0.01 versus 7.39+/-0.01, mean+/-SEM, P<.001). The maximal activity of the sodium-proton exchanger was higher in hypertensive patients than in normotensive subjects (1262+/-100 versus 851+/-56 mmol/L cells per hour, P<.01). NHE-1 mRNA was increased in hypertensive patients compared with normotensive subjects (ratio of NHE-1 mRNA to p-actin mRNA, 0.16+/-0.01 versus 0.12+/-0.02, P<.05). These data suggest that the increased sodium-proton exchange activity in essential hypertension may be related to the de novo synthesis of exchanger protein.