KINETICS OF NA+ H+ EXCHANGE IN VASCULAR SMOOTH-MUSCLE CELLS FROM WKY AND SHR - EFFECTS OF PHORBOL ESTER/

The kinetic properties of Na+/H+ exchange were investigated in vascula r smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity wa s measured in '-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were perform ed without (control) and with pretreatment of the cells with phorbol 1 2-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differe d between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (V-max) values (55 .85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+ 1(-l) min(-1)) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WK Y VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting V-max (31.88 +/- 1.55 mmol H+ 1(-1) min(-1)). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport act ivity in VSMC from SHR compared with WKY, i.e., increased V-max and de creased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked de gree of antiporter prestimulation in this animal model of genetic hype rtension.