Effects of altering carbohydrate metabolism on energy status and contractile function of vascular smooth muscle.

Substrate-dependent changes in vascular smooth muscle energy metabolism and contractile function were investigated in isolated porcine carotid arteries. In media containing glucose glycogen catabolism accounted for all the estimated high-energy phosphate turnover that occurred in conjunction with contraction induced by 80 mM KCl. However, in glucose-free media glycogen catabolism accounted for only a portion of the estimated ATP utilization in resting and contracting arteries, even though glycogen stores were not depleted. The glycogenolysis and lactate production that ordinarily accompanies contraction was completely inhibited by 5 mM 2-deoxyglucose (2-DG). However, there was no decrease in the high-energy phosphate levels when compared to control resting arteries similarly treated with 2-DG. The results suggest that an endogenous non-carbohydrate source may be an important substrate for energy metabolism. Treatment of arteries with 50 microM iodoacetate (IA) in media containing glucose resulted in a marked reduction of high energy phosphate levels and an accumulation of phosphorylated glycolytic intermediates, as demonstrated by 31P-NMR spectroscopy. In glucose-free media, 50 microM IA had only a slight effect on high-energy phosphate levels, while glycogenolysis proceeded unhindered. With 1 mM IA in glucose-free media, the oxidative metabolism of glycogen was inhibited as evidenced by the depletion of high-energy phosphates and the appearance of sugar phosphates in the 31P-NMR spectra. Thus, the titration of enzyme systems with IA reveals a structural partitioning of carbohydrate metabolism, as suggested by previous studies.