Exercise induces rapid increases in GLUT4 expression, glucose transport capacity, and insulin-stimulated glycogen storage in muscle.

J.M Ren,C.F Semenkovich,E.A Gulve,J Gao,J.O Holloszy

doi:10.1016/s0021-9258(17)36636-x

Abstract

GLUT4 glucose transporter content and glucose transport capacity are closely correlated in skeletal muscle. In this study, we tested the hypothesis that a rapid increase in GLUT4 expression occurs as part of the early adaptive response of muscle to exercise and serves to enhance glycogen storage. Rats exercised by swimming had a approximately 2-fold increase in GLUT4 mRNA and a 50% increase in GLUT4 protein expression in epitrochlearis muscle 16 h after one prolonged exercise session. After a 2nd day of exercise, muscle GLUT4 protein was increased further to approximately 2-fold while there was no additional increase in GLUT4 mRNA. Muscle hexokinase activity also doubled in response to 2 days of exercise. Glucose transport activity maximally stimulated with insulin, contractions, or hypoxia was increased roughly in proportion to the adaptive increase in GLUT4 protein in epitrochlearis muscles. Treatment with insulin prior to subcellular fractionation of muscle resulted in a approximately 2-fold greater increase in GLUT4 content of a plasma membrane fraction in the 2-day swimmers than in controls. When epitrochlearis muscles were incubated with glucose and insulin, glycogen accumulation over 3 h was twice as great in muscles from 2-day swimmers as in control muscles. Our results show that a rapid increase in GLUT4 expression is an early adaptive response of muscle to exercise. This adaptation appears to be mediated by pretranslational mechanisms. We hypothesize that the physiological role of this adaptation is to enhance replenishment of muscle glycogen stores.

Highlights

GLUT4 glucose transporter content angdlucosetrans- dant GLUT1 isoform appears to be located primarily in the port capacity are closely correlated in skeletal muscle. plasma membrane andto play a role in basal, but not insuolrin
We tested the hypothesis that a rapidin- contraction-stimulated, glucose transport [9, 11].The GLUT4 crease in GLUT4 expression occursas part of the early protein content of skeletal muscles varies markedly between adaptive response of muscle to exercise and serves to fiber types [10, 13, 14]
An control muscles.Our results show that a rapid increase adaptation that takes6 weeks to occur would generally be an in GLUT4 expression is an early adaptive response of irrelevant response tao sudden environmental change that nemuscle to exercise

Summary

Introduction

GLUT4 glucose transporter content angdlucosetrans- dant GLUT1 isoform appears to be located primarily in the port capacity are closely correlated in skeletal muscle. plasma membrane andto play a role in basal, but not insuolrin. Expression of muscle GLUT4 mRNA was nificantly greater inepitrochlearis muscles of 2-day swimmers increased -2-fold in response to 1day of swimming, and a 2nd than inthose of non-exercised controls.

Results

Conclusion