GLUCOSE-INDUCED CHANGES IN NA+/H+ ANTIPORT ACTIVITY AND GENE-EXPRESSION IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS - ROLE OF PROTEIN-KINASE-C

Increased Na+/H+ antiport activity has been implicated in the pathogenesis of hypertension and vascular disease in diabetes mellitus. The independent effect of elevated extracellular glucose concentrations on Na+/H+ antiport activity in cultured rat vascular smooth muscle cells(VSMC) was thus examined. Amiloride-sensitive Na-22(+) uptake by VSMC significantly increased twofold after 3 and 24 h of exposure to high glucose medium(20 mM) vs. control medium(5 mM). Direct glucose-induced Na+/H+ antiport activation was confirmed by measuring Naf-dependent intracellular pH recovery from intracellular acidosis. High glucose significantly increased protein kinase C (PKC) activity in VSMC and inhibition of PKC activation with H-7, staurosporine, or prior PKC downregulation prevented glucose-induced increases in Na+/H+ antiport activity in VSMC. Northern analysis of VSMC poly A(+) RNA revealed that high glucose induced a threefold increase in Na+/H+ antiport(NHE-1) mRNA at 24 h. Inhibiting this increase in NHE-1 mRNA with actinomycin D prevented the sustained glucose-induced increase in Na+/H+ antiport activity. In conclusion, elevated glucose concentrations significantly influence vascular Na+/H+ antiport activity via glucose-induced PKC dependent mechanisms, thereby providing a biochemical basis for increased Na+/H+ antiport activity in the vascular tissues of patients with hypertension and diabetes mellitus.