[en] The binding of ouabain and K⁺ to the Na⁺ pump were analyzed in serially passed cultured vascular smooth muscle cells (VSMCs) originating from spontaneously hypertensive (SH) Wistar-Kyoto (WKY), and American Wistar (W) rats. The techniques have utilized analyses of displacement of [³H]ouabain by both unlabeled ouabain and K⁺ from specific binding sites on the VSMCs. The authors have found that 1) each of the VSMC preparations from the three rat strains appeared to demonstrate one population of specific ouabain receptors (Na⁺ pumps); 2) the number of Na⁺ pump units of both the SH and WKY rats was significantly lower than the number of Na⁺ pump units of W rat VSMCs; 3) the equilibrium dissociation constant values (μM) for ouabain in VSMCs of SH and WKY rats were similar but were significantly higher than that of VSMCs derived from W rats; and 4) among the VSMCs originating from the three rat strains, the apparent equilibrium dissociation constant value for K⁺ (mM) was the lowest in those of the SH rat compared with VSMCs of the WKY rat and W rat. Previous studies have demonstrated increased passive Na⁺ and K⁺ transport rate constants of SH rat VSMCs compared with either W or WKY rat cells. These findings suggest the possibility of higher permeabilities of the SH cells. They propose that the combined effect of a low number of Na⁺ pump units with higher permeabilities to Na⁺ and K⁺ predisposes VSMCs of the SH rat to disturbances in their cellular ionic regulation. These genetic defects, if they occur in vivo, may lead to an increase in the vascular tone