Direct measurement of sodium influx in vascular smooth muscle. Stimulation by aldosterone.

The influx of 22Na into the smooth muscle cells of incubated rat tail arteries was measured directly, in the presence and absence of 2.8 X 10(-7) M D-aldosterone. During the analysis, extracellular 22Na and 23Na were removed by incubation of the tissue in sodium-free lithium-substituted physiological salt solution at less than 3 degrees C. Aldosterone increased the influx rate coefficient by 10% (0.104 +/- 0.004 [SE] min-1, n = 13, vs 0.095 +/- 0.003 [SE] min-1, n = 13 without aldosterone; p less than 0.01) but did not significantly reduce the sodium content. We conclude from direct measurements that aldosterone acts to increase the influx of sodium in incubated tail arteries from normal rats; we conclude from measurements of the sodium influx and sodium content that aldosterone also acts to increase the efflux of sodium in this preparation.