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.
- glucose transport
- insulin sensitivity and insulin resistance
- Copyright © 2016, American Journal of Physiology-Endocrinology and Metabolism