SUBSTRATE-DEPENDENT ALTERATION IN O-2 CONSUMPTION AND ENERGY-METABOLISM IN VASCULAR SMOOTH-MUSCLE

Energy metabolism and the substrate utilization pattern of intact porc ine carotid artery were investigated in the presence or absence of glu cose and/or octanoate during the phases of isometric contraction induc ed by K+ depolarization. During the early phase of contraction, there was a rapid increase in the rate of O-2 uptake that was independent of the rate of force generation but dependent on the availability of int racellular pyruvate, the source of which was glucose and not glycogen. Lactate production increased linearly from the onset of contractile s timulation and was not suppressed by octanoate oxidation. There was no alteration from the basal resting state in the concentrations of the metabolites of the tricarboxylic acid cycle in the presence or absence of octanoate. During the phase of steady-state force maintenance, O-2 consumption was increased compared with the basal unstimulated rate b ut was not increased when glucose and octanoate were present, which is consistent with the Crabtree effect. This was associated with increas ed aerobic lactic acid production and inhibition of the tricarboxylic acid cycle at the citrate synthase step. Alteration of the high-energy phosphate content could not account for the pattern of O-2 consumptio n during contraction under different substrate conditions. In the abse nce of glucose, the energy from octanoate oxidation could substitute f or the energy ordinarily derived from aerobic glycogen and lactic acid production. It is concluded that energy metabolism of vascular smooth muscle is coordinated during contraction by integration of the pathwa ys of aerobic glycolysis and oxidative phosphorylation.