Effect of potassium on isolated bovine facial and human saphenous veins.

A moderate elevation of external (K0+) (5--10 mM) induces relaxation in bovine facial and human saphenous veins. A further increase of (K0+) leads to biphasic reactions (relaxation followed by contraction). Concentrations of (K0+) higher than about 15 mM cause contractions only. The potassium-induced relaxation may be explained by the stimulation of an electrogenic sodium pump.