“…The hyperpolarization induced by histamine may be due to an increased K + conductance that is mediated by an increased Ca 2+ influx, since inhibition of Ca THE effects of histamine on vascular smooth muscle (VSM) are highly variable and range from excitation to inhibition to no effect (Broadley, 1975;Carrier, 1965;Reite, 1972;Altura and Altura, 1974;Hudgins and Weiss, 1968). When injected into the beating dog heart, histamine causes a marked in-crease in coronary blood flow (Giles et al, 1977) suggesting a vasodilation. However, when added to the bathing solution of isolated coronary arteries of dog (Carrier, 1965), swine, and man (Smith et al, 1951), histamine causes a vasoconstriction.…”