NA-H+ ANTIPORTER PHENOTYPE, ABUNDANCE, AND PHOSPHORYLATION OF IMMORTALIZED LYMPHOBLASTS FROM HUMANS WITH HYPERTENSION()

Previous studies have demonstrated an elevated Na+-H+ exchanger activi ty in various cell types from patients with essential hypertension. Th e phenotype of an increased maximal transport capacity is preserved in Epstein-Barr virus immortalized lymphoblasts from hypertensive patien ts. The mechanisms underlying this abnormality are unclear. In this st udy, 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) Nac-Hc exchanger isoform 1 abundance with specific polyclonal antibodies, and (3) Na+-H+ exchanger phosphorylation by immunoprecipitation of the P- 32-labeled transporter. Na+-H+ exchanger activity (in millimoles per l iter per minute) measured when pH(i) was clamped at 6.0 was significan tly higher in cells from hypertensive patients (18.8+/-0.6, P<.001) an d those subjects with a family history of hypertension (16.4+/-0.6, P< .001) compared with normotensive control subjects (12.9+/-0.6). Exchan ger abundance was identical in all three groups of subjects, indicatin g that increased activity in the hypertensive group was due to an elev ated turnover number of the exchanger. Na+-H+ exchanger phosphorylatio n in quiescent cells was significantly elevated in cells from hyperten sive patients (1.58+/-0.16, P<.001) compared with control subjects (1. 00+/-0.07), and cells from normotensive subjects with a hypertensive f amily history showed intermediate values (1.23+/-0.14). Identical chan ges in Na+-H+ exchanger function and phosphorylation have been demonst rated in vascular smooth muscle cells from spontane ously hypertensive rats. Our findings suggest that the elevated Na+-H+ exchanger activit y in cells from human hypertensive patients is not associated with an increased exchanger abundance but may be related to increased exchange r phosphorylation.