Prostaglandins and potassium relaxation in vascular smooth muscle of the rat. The role of Na-K ATPase.
We explored the hypothesis that postaglandin-induced vasodilation is caused by activation of the electrogenic sodium-potassium pump which results in membrane hyperpolarization and relaxation of vascular smooth muscle. Helical strips of rat tail artery relax in response to potassium after norepinephrine-induced contractions in physiological salt solution containing a low-potassium concentration. The amplitude of this potassium relaxation is used as an index of sodium-potassium ATPase activity. It was observed that PGA1, PGE2, and PGF2alpha (10(-6) g/ml) significantly enhanced the magnitut. PGE2 caused relaxation of contractions induced by either 25 mM KCl or norepinephrine (10(-9) g/ml), and these relaxations were inhibited by 10(-4) M ouabain. Indomethacin (5.3 x 10(-6) g/ml) and meclofenamate (10(-6) g/ml) reduced the magnitude of potassium-induced relaxation by more than 30% of control. PGF2alpha (10(-5) g/ml) reversed the inhibition of potassium relaxation by meclofenamate. These observations suggest that prostaglandins induce vascular smooth muscle relaxation by stimulation of the sodium pump and that endogenous prostaglandins normally potassium relaxation.