The effects of isoproterenol and ouabain on oxygen consumption, lactate production, and the activation of phosphorylase in coronary artery smooth muscle.

In previous work, oxidative metabolism in vascular smooth muscle was found to be correlated with isometric force; aerobic lactate production, however, was found to be substantial and correlated with Na-K transport processes (Paul et al., 1979; Paul, 1980). In this work, the role of glycogen phosphorylase in this unusual functional compartmentalization of of vascular energy metabolism was investigated. Isometric force, oxygen consumption, lactate production, and the level of phosphorylase activity were measured in porcine coronary arterial segments. For comparison with previous studies, phosphorylase activity was also measured in rabbit aorta. Added potassium chloride induced a contracture in which oxygen consumption, lactate production, and phosphorylase activity all increased. Ouabain also induced a contracture, and an increase in oxygen consumption and phosphorylase activity. However, lactate production was inhibited. Isoproterenol, when added to a potassium chloride-induced contracture, elicited a relaxation in isometric force, and oxygen consumption returned to basal levels; however, lactate production and phosphorylase activity remained at the previously elevated levels. Isoproterenol alone had only marginal effects on all parameters studied. The results indicate that the role of phosphorylase in vascular metabolism is complex and unlikely to be a rate-limiting factor for the observed aerobic glycolysis. The high levels of phosphorylase activity observed in the absence of actomyosin interaction support a mechanism of beta-adrenergic relaxation in which the sensitivity of actin-myosin interaction to calcium ion is decreased.