Novel single skeletal muscle fiber analysis reveals a fiber type-selective effect of acute exercise on glucose uptake.
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 postexercise (IPEX) would be characterized by increased insulin-dependent glucose uptake at 3.5 h postexercise (3.5hPEX). Rat epitrochlearis muscles were isolated and incubated with 2-[3H]deoxyglucose. Muscles from IPEX and sedentary (SED) controls were incubated without insulin. Muscles from 3.5hPEX and SED controls were incubated ± insulin. Glucose uptake (2-[3H]deoxyglucose accumulation) and fiber type (myosin heavy chain isoform expression) were determined for single fibers dissected from the muscles. Major new findings included the following: 1) insulin-independent glucose uptake was increased IPEX in single fibers of each fiber type (types 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 vs. SED had greater insulin-stimulated glucose uptake in type I, IIA, IIB, and IIBX but not type IIX fibers. Insulin-dependent glucose uptake was increased at 3.5hPEX in each fiber type except for IIX fibers, although insulin-independent glucose uptake was increased IPEX in all fiber types (including type IIX). Single fiber analysis enabled the discovery of this fiber type-related difference for postexercise, insulin-stimulated glucose uptake.
Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, Michigan; gcartee@umich.edu.|Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan; and.|Institute of Gerontology, University of Michigan, Ann Arbor, Michigan.
Gregory D
GD
Cartee
Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, Michigan.
Edward B
EB
Arias
Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, Michigan.
Carmen S
CS
Yu
Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, Michigan.
Mark W
MW
Pataky
D000818:Animals; D003847:Deoxyglucose / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005947:Glucose / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010805:Physical Conditioning, Animal; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014316:Tritium
D007004:Hypoglycemic Agents; D007328:Insulin; D020033:Protein Isoforms; D014316:Tritium; D003847:Deoxyglucose; D018995:Myosin Heavy Chains; D005947:Glucose
exercise; glucose transport; insulin sensitivity and insulin resistance