Effects of Calorie Restriction and Fiber Type on Glucose Uptake and Abundance of Electron Transport Chain and Oxidative Phosphorylation Proteins in Single Fibers from Old Rats

Calorie restriction (CR; reducing calorie intake by ~40% below ad libitum) can increase glucose uptake by insulin-stimulated muscle. Because skeletal muscle is comprised of multiple, heterogeneous fiber types, our primary aim was to determine the effects of CR (initiated at 14 weeks old) and fiber type on insulin-stimulated glucose uptake by single fibers of diverse fiber types in 23-26-month-old rats. Isolated epitrochlearis muscles from AL and CR rats were incubated with [3H]-2-deoxyglucose ± insulin. Glucose uptake and fiber type were determined for single fibers dissected from the muscles. We also determined CR-effects on abundance of several key metabolic proteins in single fibers. CR resulted in: (a) significantly (p < .05 to .001) greater glucose uptake by insulin-stimulated type I, IIA, IIB, IIBX, and IIX fibers; (b) significantly (p < .05 to .001) reduced abundance of several mitochondrial electron transport chain (ETC) and oxidative phosphorylation (OxPhos) proteins in type I, IIA, and IIBX but not IIB and IIX fibers; and (c) unaltered hexokinase II abundance in each fiber type. These results demonstrate that CR can enhance glucose uptake in each fiber type of rat skeletal muscle in the absence of upregulation of the abundance of hexokinase II or key mitochondrial ETC and OxPhos proteins.