Design and methodsLevels of dietary and serum potassium are thought to correlate inversely with vascular resistance and blood pressure. This study examined renal vascular resistance in perfused rat kidneys partially preconstricted with 10 μmol/l phenylephrine, quantifying changes in the resistance when levels of potassium in the perfusate ([K+]0) were varied between 2 and 80 mmol/l.ResultsIn kidneys from 17-week-old Wistar–Kyoto rats (WKY strain) fed a normal diet (American Institute of Nutrition AIN-76 diet), the resistance decreased when [K+]0was raised from 4 to 6–20 mmol/l, whereas resistance increased when [K+]0was either lowered to 2 mmol/l or raised above 25 mmol/l. The vasodilation that occurred at 13 mmol/l [K+]0was blocked by 100 μmol/l BaCl2and 10 μmol/l ouabain in an additive manner, suggesting that both the inward rectifier K+channel and the Na-K-ATPase underlie the dilation. Kidneys from spontaneously hypertensive rats (SHR strain) fed the AIN-76 diet displayed modestly enhanced vasodilations and vasoconstrictions as compared to WKY. A high-potassium diet (AIN-76 supplemented with 3.5% potassium citrate, provided for 8 weeks) led to exaggerated vasoconstrictive effects of [K+]0, and modestly enhanced vasodilations, in WKY rats. In contrast, the diet led to attenuated vasoconstrictions, and dramatically enhanced vasodilations, in the SHR strain. The diet did not affect the blood pressure increase or weight gain of either strain.ConclusionsChanges in the responsiveness of blood vessels to extracellular potassium might underlie some beneficial effects of high-potassium diets in hypertensive individuals.