Influence of glycogen storage on vascular smooth muscle metabolism

Abstract

The role of glycogen as an oxidative substrate for vascular smooth muscle (VSM) remains controversial. To elucidate the importance of glycogen as an oxidative substrate and the influence of glycogen flux on VSM substrate selection, we systematically altered glycogen levels and measured metabolism of glucose, acetate, and glycogen. Hog carotid arteries with glycogen contents ranging from 1 to 11 μmol/g were isometrically contracted in physiological salt solution containing 5 mM [1-13C]glucose and 1 mM [1,2-13C]acetate at 37°C for 6 h. [1-13C]glucose, [1,2-13C]acetate, and glycogen oxidation were simultaneously measured with the use of a 13C-labeled isotopomer analysis of glutamate. Although oxidation of glycogen increased with the glycogen content of the tissue, glycogen oxidation contributed only ∼10% of the substrate oxidized by VSM. Whereas [1-13C]glucose flux, [3-13C]lactate production from [1-13C]glucose, and [1,2-13C]acetate oxidation were not regulated by glycogen content, [1-13C]glucose oxidation was significantly affected by the glycogen content of VSM. However, [1-13C]glucose remained the primary (∼40–50%) contributor to substrate oxidation. Therefore, we conclude that glucose is the predominate substrate oxidized by VSM, and glycogen oxidation contributes minimally to substrate oxidation.