GLUCOSE-INDUCED CHANGES IN ACTIVITY AND PHOSPHORYLATION OF THE NA+ H+EXCHANGER, NHE-1, IN VASCULAR MYOCYTES FROM WISTAR-KYOTO AND SPONTANEOUSLY HYPERTENSIVE RATS/

Increased Na+/H+ exchanger (NHE) activity has been demonstrated in cel ls from patients with hypertension and diabetic nephropathy. Vascular myocytes from the spontaneously hypertensive rat (SHR) also exhibit in creased NHE activity as compared with cells from the normotensive Wist ar Kyoto rat (WKY). The interaction of increased glucose concentration s with NHE activity is unclear. The effect of glucose on NHE activity, NHE-1 (isoform 1) protein expression, and phosphorylation of cultured vascular myocytes from these rat strains was thus investigated. NHE a ctivity was determined fluorometrically with 2',7'-bis(2-carboxyethyl) -5(6)-carboxyfluorescein (BCECF). A rabbit NHE-1-specific polyclonal a ntibody was used (1) to measure NHE-1 abundance in Western blots of ce ll extracts and (2) for immunoprecipitating P-32-labeled NHE 1. Cells from SHR exhibited increased NHE activity and NHE-1 phosphorylation as compared with cells from WKY, with similar NHE-1 protein content per cell. Incubation in 25 mmol . L(-1) glucose for 24 hours led to increa sed NHE activity only in WKY cultures, with no change in NHE-1 protein but a concomitantly reduced NHE-1 phosphorylation. Changes in NHE act ivity in WKY cells were reversed by inhibition of protein kinase C. In cubation of SHR cells with 25 mmol . L(-1) glucose did not enhance the increased NHE activity or NHE-1 phosphorylation present in these cell s. Thus, high glucose levels have disparate effects on NHE activity an d NHE-1 phosphorylation in cells from different rat strains. The gluco se-induced increase in NHE-1 turnover number in WKY cells is not media ted by an increase in its direct phosphorylation, but is dependent on protein kinase C. Copyright (C) 1996 by W.B. Saunders Company