Effect of respiratory muscle training on GLUT-4 in the sheep diaphragm.
OBJECTIVE
Endurance exercise training is associated with enhanced glucose uptake and hence improvement in carbohydrate metabolism. Glucose transport (GLUT) membrane proteins are regulated by a variety of physiological stimuli, including exercise. In limb muscle, both acute exercise and endurance training enhance the expression of the skeletal muscle transporter, GLUT-4. The purpose of this study is to determine whether chronic loading enhances GLUT-4 expression in the diaphragm.


METHODS
The effect of chronic inspiratory flow resistive (IFR) loading on diaphragm GLUT-4 was studied in a model of respiratory muscle endurance training in sheep. IFR loads (resistance 50-100 cm H2O x L(-1) x s(-1)) were maintained for 3 h x d(-1), 5-6 d x wk(-1) for 3 wk. Loading was adjusted so that PaO2 was >60 Torr and PaCO2 <45 Torr in room air. Six untrained sheep were used as controls. GLUT-4 protein and mRNA were analyzed by Western and Northern analysis respectively.


RESULTS
GLUT-4 protein levels were two-fold greater in trained animals when compared with controls (P < 0.01). GLUT-4 mRNA levels in the trained muscles was not significantly different from controls.


CONCLUSIONS
We conclude that in the sheep diaphragm, chronic IFR loading increases GLUT-4 protein levels. This increase may be one of the mechanisms contributing to the improved respiratory muscle endurance previously demonstrated in this animal model of respiratory muscle training.
Bhandari
A
A
Department of Pediatrics, Yale University School of Medicine, New Haven, CT 06510, USA.
Xia
Y
Y
Cortright
R
R
Dohm
G L
GL
Bazzy
A R
AR
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D001945:Breathing Exercises; D003964:Diaphragm / Q000378:metabolism* / Q000502:physiology; D051275:Glucose Transporter Type 4; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D012333:RNA, Messenger / Q000097:blood; D012756:Sheep
D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases