Mechanical responses of isolated dog cerebral arteries to reduction of external K, Na, and Cl.

Reduction of the extracellular potassium concentration ([K+]0) caused a significant contraction in helical strips of dog cerebral arteries, but only a slight contraction, or none, in peripheral (coronary, mesenteric, renal, and femoral) arteries. The cerebroarterial contraction was abolished by treatment with ouabain or by substitution of Li+ for Na+, and suppressed by exposure to Ca2+-free media or verapamil. When one-half of the NaCl of the bathing solution was substituted with choline chloride a moderate, sustained contraction was produced in cerebral and peripheral arteries. Ouabain potentiated this contraction, whereas exposure to Ca2+-free media abolished it. Substitution of Na propionate, NaI, or Na acetylglycinate for one-half of the NaCl elicited a marked, transient contraction in only the cerebral arteries. This contractile response was potentiated by ouabain and markedly attenuated by exposure to Ca2+-free media. It may thus be concluded that cerebroarterial contractions induced by a reduction in [K+]0 are due to inhibition of the electrogenic Na+ pump, which results in depolarization of smooth muscle cells. Substitution of Cl- with less permeant anions appears to produce cerebroarterial contraction in association with depolarization of smooth muscle cells.