Effect of serum on cell membrane Na-K transport of vascular smooth muscle in culture--a comparative study between normotensive and hypertensive rats.

In order to elucidate the effect of serum and its differential characteristics in primary hypertension, we investigated the influence of serum from spontaneously hypertensive rats (SHR) on the cell membrane Na-K pump, Na-H antiport and passive K permeability of cultured vascular smooth muscle cells (VSMC) from SHR and Wistar-Kyoto rats (WKY). In the absence of serum, the Na-K pump activity, described as ouabain-sensitive 86Rb uptake (OS), was greater in the VSMC of the SHR than that of the WKY. Addition of serum to the quiescent VSMC stimulated the OS, of which activation was significantly greater with the SHR serum than with the WKY serum. Determination of intracellular Na concentrations in the presence of 1 mM ouabain showed that Na uptake in the absence of serum of the SHR VSMC was greater than that of the WKY VSMC. Subjecting the VSMC to rat serum stimulated Na uptake, which effect was more profound with SHR serum than with WKY serum. A greater stimulation of 5-(N,N-hexamethylene) amiloride(HMA)-sensitive Na uptake by SHR serum accounted for this difference. When the Na-K pump was active, intracellular Na concentrations were unchanged in the presence of serum. Furthermore, serum from either of the two strains produced a substantial increase in the washout rate constant of 86Rb washout (Ke), which effect was also larger in SHR serum than in WKY serum. In the absence of serum, basal Ke of the SHR VSMC was greater than that of the WKY VSMC. It is concluded that serum from SHR produced a more pronounced activation of the Na-K pump, Na-H antiport and passive K permeability in cultured VSMC. The study suggests that in addition to an innate augmented activity of Na-K transporters in the VSMC of SHR, there are humoral factors in SHR serum which elicit the stimulation of the Na-H antiport, leading to either the activation of the Na-K pump or secondary stimulation of passive K permeability across the cell membrane.