Vascular sodium pump activity kinetics in early and advanced stages of deoxycorticosterone-salt hypertension in rats.

We determined the kinetic properties--the maximal velocity, Vmax, and the half-maximal activating concentration of K+, km values--of the vascular sodium pump in rats 6, 28, and 50 days after deoxycorticosterone and sodium chloride (DOC-salt) or vehicle treatment. Tail arteries from six or eight rats from each treatment group were pooled, and Na-pump activity was measured in a Krebs medium containing varying K+ (plus 86Rb+) concentrations (0.25-10 mM). Na-pump activity was plotted as a function of [K + 86Rb]. Data were fit to a two-site model to calculate Vmax and km values. Systolic blood pressures were normal after 6 days but high after 28 and 50 days of DOC-salt treatment. No difference in kinetic parameters existed between the treatment and control groups 6 and 50 days after DOC-salt treatment. After 28 days, Vmax was significantly elevated compared with controls; km was not affected. Thus, stimulation of the vascular Na-pump during established hypertension is due to an increase in the maximal velocity of ouabain-sensitive uptake of K+.