Ion-selective electrode studies of cell Na components in vascular smooth muscle of WKY and SHR.

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Vascular smooth muscle cells of the rat tail artery were enriched with Na by overnight incubation at 10 degrees C in K-free physiological salt solution (K-free PSS). The cells were then returned to normal PSS in a series of steps so as to define the effect of varying temperature between 3 and 37 degrees C, the effect of ouabain, the effect of readmitting K+ in the continuing presence of ouabain, and, finally, the effect of removing ouabain in the continuing presence of K+. The effects were measured with flow-through Na+ and K+ glass-cannula electrodes as changes in a superfusate moving slowly past the artery. Where possible, confirmatory evidence was obtained by conventional incubations followed by chemical analysis of the tissues. About 10 mmol Na+/kg dry wt is transferred out of the cells when temperature is raised from 3 to 37 degrees C. Exposure of the tissue to ouabain while the tissue is still in the K-free state produces a further loss of about 8 mmol Na+/kg dry wt and 4 mmol k+/kg dry wt. Readmittance of K+ in the continuing presence of ouabain induces a further loss of about 25 mmol Na+/kg dry wt in exchange for an uptake of about 13 mmol K+ measured electrometrically or about 20 mmol K measured chemically. Finally, the removal of ouabain is followed by an extrusion of about 155 mmol Na+/kg dry wt in exchange for an uptake of 133 mmol K%. The ouabain-insensitive exchange of Na+ and K+ is enhanced in spontaneously hypertensive rats as compared with normotensive rats.