Potassium-free solution prevents the action but not the release of endothelium-derived relaxing factor.

Exposure to a K+-free solution reversibly inhibited the acetylcholine-induced relaxation in perfused canine femoral artery segments with endothelium and in superfused bioassay femoral artery rings without endothelium. Infusion of 6.7 mM K+ into the K+-free perfusate downstream of the perfused artery restored the acetylcholine-induced relaxation in the bioassay ring, whereas no relaxation was observed in the perfused segment still exposed to the K+-free solution. These data demonstrate that the K+-free solution depresses the endothelium-dependent relaxation to acetylcholine in femoral arteries by preventing the action, but not the production, of endothelium-derived relaxing factor.