Stimulatory effect of serum on 86Rb washout from vascular smooth muscle cells in culture.

Summary In order to elucidate the effect of serum on passive K permeability of vascular smooth muscle cells (VSMC) membrane, outward passive K permeability yielded as washout rate constant ( K e ) of 86 Rb washout, was measured in the presence and in the absence of cation transport modulators using VSMC in culture. The overall K e of 86 Rb washout subjected to 1% serum was significantly larger than that in controls. This stimulated K e was substantially blunted in the presence of 10 −4 m amiloride and was partially inhibited with 5 × 10 −4 m bumetanide. Angiotensin II of 10 −5 m exerted to a lesser extent, a similar significant stimulatory effect on K e of 86 Rb washout, which effect was inhibited with application of amiloride. Additionally, Ca-antagonist, 10 −5 m nifedipine reduced serum-stimulated K e to the basal level. It is concluded that both serum and angiotensin II increase K permeability in cultured VSMC. A part of this effect of serum may be attributable to angiotensin II in the serum. Furthermore, it is suggested that the stimulatory effect of serum on membrane permeability may be exerted, at least in part, via activation of both Na-H antiport and Na-K co-transport, possibly through mechanisms in conjunction with intracellular Ca.