Effects of exercise and glucose administration on content of insulin-sensitive glucose transporter in equine skeletal muscle.
OBJECTIVE
To characterize insulin-sensitive glucose-transporter (GLUT-4) protein in equine tissues and determine effects of exercise and glucose administration on content of GLUT-4 protein in equine skeletal muscle.


METHODS
Tissue samples from 9 horses.


METHODS
Western blot analyses were performed on crude membrane preparations of equine tissues to characterize GLUT-4. In a crossover, randomized study, horses were strenuously exercised for 3 consecutive days and then administered 13.5% glucose or isotonic saline (0.9% NaCl; control) solution, i.v., at similar infusion rates for 12.1 hours. Samples were collected from the middle gluteal muscle before and after exercise and 10.1 hours after completion of an infusion and used for measurements of glycogen concentration and total content of GLUT-4 protein.


RESULTS
Immunoblot analyses detected specifically immunoreactive bands for GLUT-4 in insulin-sensitive tissues. Content of GLUT-4 protein in skeletal muscle increased significantly by 27.3 and 12.3% 22.2 hours after exercise for control and glucose groups, respectively. Intravenous infusion of glucose resulted in a significantly higher rate of glycogenesis, compared with results for the control group (mean +/- SD, 3.98 +/- 0.61 and 1.47 +/- 0.20 mmol/kg/h, respectively). Despite enhanced glycogenesis, we did not detect an increase in content of GLUT-4 protein after glucose infusion, compared with values after exercise.


CONCLUSIONS
GLUT-4 protein was expressed in equine skeletal and cardiac muscles. Exercise increased total content of GLUT-4 protein in skeletal muscle, and replenishment of muscle glycogen stores after glucose infusion attenuated the exercise-induced increase in the content of GLUT-4 protein in equine skeletal muscle.
Lacombe
Véronique A
VA
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA.
Hinchcliff
Kenneth W
KW
Devor
Stephen T
ST
D000818:Animals; D015153:Blotting, Western; D005947:Glucose / Q000494:pharmacology*; D051275:Glucose Transporter Type 4; D006736:Horses / Q000502:physiology*; D009004:Monosaccharide Transport Proteins / Q000187:drug effects* / Q000502:physiology; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*
D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D005947:Glucose