Novel Single Skeletal Muscle Fiber Analysis Reveals a Fiber Type Selective Effect of Acute Exercise on Glucose Uptake
AJP Endocrinology and Metabolism
Published online on September 06, 2016
Abstract
One exercise session can induce subsequently elevated insulin sensitivity that is largely attributable to greater insulin-stimulated glucose uptake by skeletal muscle. Because skeletal muscle is a heterogeneous tissue comprised of diverse fiber types, our primary aim was to determine exercise effects on insulin-independent and insulin-dependent glucose uptake by single fibers of different fiber types. We hypothesized that each fiber type featuring elevated insulin-independent glucose uptake immediately post-exercise (IPEX) would be characterized by increased insulin-dependent glucose uptake at 3.5h post-exercise (3.5hPEX). Rat epitrochlearis muscles were isolated and incubated with [3H]-2-deoxyglucose. Muscles from IPEX and sedentary (SED) controls were incubated without insulin. Muscles from 3.5hPEX and SED controls were incubated ±insulin. Glucose uptake ([3H]-2-deoxyglucose accumulation) and fiber type (myosin heavy chain isoform expression) were determined for single fibers dissected from the muscles. Major new findings included: 1) insulin-independent glucose uptake was increased IPEX in single fibers of each fiber type (I, IIA, IIB, IIBX and IIX); 2) glucose uptake values from insulin-stimulated type I and IIA fibers exceeded the values for the other fiber types; 3) insulin-stimulated glucose uptake for type IIX exceeded IIB fibers; and 4) the 3.5hPEX group versus SED had greater insulin-stimulated glucose uptake in type I, IIA, IIB and IIBX, but not IIX fibers. Insulin-dependent glucose uptake was increased at 3.5hPEX in each fiber type except IIX fibers even though insulin-independent glucose uptake was increased IPEX in all fiber types (including IIX). Single fiber analysis enabled the discovery of this fiber type-related difference for post-exercise, insulin-stimulated glucose uptake.