Sodium cotransport in vascular smooth muscle cells.

Vascular smooth muscle cells possess a number of Na cotransport systems. Three of these cotransport systems, Na/Ca exchange, Na/H exchange and Na-K-Cl cotransport, have been the subject of an increasing number of investigations to determine the respective roles of these transporters in vascular smooth muscle cell function. Evidence has been obtained that the Na/Ca exchange system participates in regulation of intracellular Ca in vascular smooth muscle cells. The Na/H exchange system appears to function in concert with a Cl/HCO3 exchange system to regulate intracellular pH. The Na-K-Cl cotransport system is a major contributor to K flux across the plasma membrane of vascular smooth muscle cells and is regulated by a number of vasoactive agents, suggesting that this Na cotransport system is also an important component of vascular smooth muscle cell function. Cultured vascular smooth muscle cells derived from spontaneously hypertensive rats have been found to exhibit reduced Na-K-Cl cotransport activity compared to smooth muscle cells from normotensive controls. Thus, alteration of vascular smooth muscle Na-K-Cl cotransport activity may be related to changes in vascular tone. However, the precise function of Na-K-Cl cotransport in vascular smooth muscle cells remains to be clarified. Recent studies of Na-K-Cl cotransport in vascular endothelial cells provide evidence that the co-transporter is important for regulation of endothelial cell volume and suggest that this Na cotransport system may be vitally important for normal function of the vasculature.