INHIBITION BY Cd2+, VERAPAMIL AND PAPAVERINE OF Ca2+‐INDUCED CONTRACTIONS IN ISOLATED CEREBRAL AND PERIPHERAL ARTERIES OF THE DOG

1 In helically cut strips of canine cerebral arteries exposed to Ca2+-free media and depolarized by K+, the addition of Ca2+ caused biphasic (transient and sustained) contractions, while in coronary and mesenteric arteries, the additon of Ca2+ produced a sustained contraction sometimes preceded by a slight transient contraction. 2. These Ca2+-induced contractions were attenuated by Cd2+ (50 to 100 micron) in a dose-dependent manner, the attenuation being greater in cerebral than in coronary and mesenteric arteries. The inhibitory effect of Cd2+ was prevented and partially reversed by 1 mM cysteine. 3. Verapamil and papaverine were also effective in attenuating the Ca2+-induced contrations in cerebral and peripheral arteries: susceptibility to verapamil was in the order, cerebral greater than coronary greater than mesenteric, while that to papaverine was in the order, cerebral=coronary greater than mesenteric. 4. It may be concluded that the agents that interfere with trans-membrane influxes of Ca2+ cause a greater relaxation in cerebral than in peripheral arteries, as is seen with papaverine, a non-specific vasodilator.