High-Fat Diet-Induced Insulin Resistance in Single Skeletal Muscle Fibers is Fiber Type Selective

Skeletal muscle is the major site for insulin-stimulated glucose disposal, and muscle insulin resistance confers many negative health outcomes. Muscle is composed of multiple fiber types, and conventional analysis of whole muscles cannot elucidate fiber type differences at the cellular level. Previous research demonstrated that a brief (two weeks) high fat diet (HFD) caused insulin resistance in rat skeletal muscle. The primary aim of this study was to determine in rat skeletal muscle the influence of a brief (two weeks) HFD on glucose uptake (GU) ± insulin in single fibers that were also characterized for fiber type. Epitrochlearis muscles were incubated with [(3)H]-2-deoxyglucose (2DG) ± 100 µU/ml insulin. Fiber type (myosin heavy chain expression) and 2DG accumulation were measured in whole muscles and single fibers. Although fiber type composition of whole muscles did not differ between diet groups, GU of insulin-stimulated whole muscles from LFD rats significantly exceeded HFD values (P < 0.005). For HFD versus LFD rats, GU of insulin-stimulated single fibers was significantly (P < 0.05) lower for IIA, IIAX, IIBX, IIB, and approached significance for IIX (P = 0.100), but not type I (P = 0.776) fibers. These results revealed HFD-induced insulin resistance was attributable to fiber type selective insulin resistance and independent of altered fiber type composition.