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

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.