Acetate or octanoate increases glycogenolysis in smooth muscle as determined by 13C-NMR

Vascular smooth muscle is considered a model system for the study of the compartmentation of carbohydrate metabolism. Since vascular smooth muscle is capable of synthesizing substantial glycogen stores and utilizing a variety of metabolic substrates, we sought to determine the effects of utilization of either acetate or octanoate on 2-13C-glucose metabolism and on 1-13C-glycogen metabolism in contracting hog carotid arteries having high levels of 13C-labeled glycogen. In carotid arteries that have been allowed to synthesize substantial amounts of glycogen (to a total content of 7.84 +/- 0.31 mumol/gm wet wt glucosyl units), provision of either 5 mM 2-13C-glucose and 2 mM sodium acetate or 5 mM 2-13C-glucose and 0.5 mM octanoic acid during a 3 hr. contraction resulted in a 74% and 71% increase in glycogen utilization compared to that in the presence of glucose as the sole exogenous substrate. The fraction of the 3-13C-lactate from 1-13C-glycogen was substantially reduced in the presence of either acetate or octanoate. We speculate that AMP production by thiokinases with localized access of AMP to phosphorylase may be the common mechanism of glycogenolytic modulation by acetate and octanoate in contracting vascular smooth muscle with high glycogen content. We conclude that utilization of exogenous fatty acids can regulate glycogenolysis independent of glycolysis in contracting vascular smooth muscle with high glycogen content.