Regulation of Contractile Responses of Vascular Smooth Muscle Cells under Conditions of Hypoxia-Reoxygenation.

We analyzed the effects of hypoxia and reoxygenation on changes in contractile activity in rat aortic smooth muscles. Both hypoxia and reoxygenation induced relaxation of smooth muscle cells precontracted with high-potassium Krebs solution (30 mM KCl) or α-adrenoceptor agonist phenylephrine. Vasodilation resulted from enhancement of potassium permeability of smooth muscle cell membranes caused by activation of voltage-gated potassium channels (triggered by both precontracting agents) or by opening of ATP-sensitive potassium channels (phenylephrine). In isolated smooth muscle cells, both hypoxia and inhibition of Na,K-ATPase with ouabain led to depletion of intracellular store of macroergic substances, reduced potassium concentration, and elevated the content of sodium ions.