Na+-H+ Antiporter Phenotype, Abundance, and Phosphorylation of Immortalized Lymphoblasts From Humans With Hypertension

Abstract Previous studies have demonstrated an elevated Na+-H+ exchanger activity in various cell types from patients with essential hypertension. The phenotype of an increased maximal transport capacity is preserved in Epstein-Barr virus immortalized lymphoblasts from hypertensive patients. The mechanisms underlying this abnormality are unclear. In this study, we used lymphoblasts from hypertensive patients and normotensive control subjects with and without a family history of hypertension to determine (1) Na+-H+ exchanger activity using fluorometry with the pH indicator 2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein, (2) Na+-H+ exchanger isoform 1 abundance with specific polyclonal antibodies, and (3) Na+-H+ exchanger phosphorylation by immunoprecipitation of the 32P-labeled transporter. Na+-H+ exchanger activity (in millimoles per liter per minute) measured when pHi was clamped at 6.0 was significantly higher in cells from hypertensive patients (18.8±0.6, P <.001) and those subjects with a family history of hypertension (16.4±0.6, P <.001) compared with normotensive control subjects (12.9±0.6). Exchanger abundance was identical in all three groups of subjects, indicating that increased activity in the hypertensive group was due to an elevated turnover number of the exchanger. Na+-H+ exchanger phosphorylation in quiescent cells was significantly elevated in cells from hypertensive patients (1.58±0.16, P <.001) compared with control subjects (1.00±0.07), and cells from normotensive subjects with a hypertensive family history showed intermediate values (1.23±0.14). Identical changes in Na+-H+ exchanger function and phosphorylation have been demonstrated in vascular smooth muscle cells from spontaneously hypertensive rats. Our findings suggest that the elevated Na+-H+ exchanger activity in cells from human hypertensive patients is not associated with an increased exchanger abundance but may be related to increased exchanger phosphorylation.