Bumetanide-sensitive sodium-22 transport in vascular smooth muscle cell of the spontaneously hypertensive rat.

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Abstract
The effect of bumetanide, a known probe of Na+, K+ cotransport, on 22Na+ uptake and washout was examined in serially passed cultured vascular smooth muscle cells of spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY), and Wistar rats. In Ca2+-deficient medium, the drug exerted the greatest effect on 22Na+ washout in vascular smooth muscle cells from SHR and the least effect on cells from WKY. The respective mean values for the apparent bumetanide-sensitive 22Na+ washout rate constants (Ke; X 10(-2)/min) were 7.2, 4.3, and 1.7 for cells from SHR, WKY, and Wistar rats. In both 1 mM Ca2+ and Ca2+-deficient medium, in the presence of 1 mM ouabain, vascular smooth muscle cells from SHR had the highest plateau phase of 22Na+ uptake among the three cell preparations. All cells exhibited higher 22Na+ uptake in Ca2+-deficient medium than in 1 mM Ca2+ medium. Under this condition, bumetanide caused an additional rise in steady state 22Na+ uptake that was most pronounced in cells from SHR (21.3% versus 16.6% for Wistar rats and 4.8% for WKY). This finding indicates that a quantitatively greater inhibition of washout than of the uptake component of the bumetanide-sensitive 22Na+ transport occurs in Ca2+-deficient medium. It is concluded that, in Ca2+-deficient medium, the bumetanide-sensitive 22Na+ washout is higher in vascular smooth muscle cells of SHR than in those of normotensive controls and that this phenomenon reflects a higher Na+ turnover in vascular smooth muscle cell in the hypertensive rat strain.