Expression of equine glucose transporter type 4 in skeletal muscle after glycogen-depleting exercise.
OBJECTIVE
To clone and sequence cDNA for equine insulin-responsive glucose transporter (glucose transporter type 4 [GLUT-4]) and determine effects of glycogen-depleting exercise and meal type after exercise on GLUT-4 gene expression in skeletal muscle of horses.


METHODS
Muscle biopsy specimens from 7 healthy adult horses.


METHODS
Total RNA was extracted from specimens, and GLUT-4 cDNA was synthesized and sequenced. Horses were exercised on 3 consecutive days. On the third day of exercise, for 8 hours after exercise, horses were either not fed, fed half of daily energy requirements as hay, or fed an isocaloric amount of corn. The GLUT-4 mRNA was determined by use of real-time reverse transcriptase-polymerase chain reaction in muscle biopsy specimens obtained before 3 consecutive days of exercise and within 10 minutes and 4, 8, and 24 hours after the third exercise bout.


RESULTS
A 1,629-bp segment was sequenced, of which 1,530 bp corresponded to the coding region end encoded a protein of 509 amino acids. Expression of GLUT-4 gene increased by 2.3, 4.3, 3.3, and 2.6 times 10 minutes and 4, 8, and 24 hours after exercise, respectively, compared with that prior to exercise. No differences were observed in GLUT-4 gene expression among conditions of feed withholding, corn feeding, and hay feeding during the 8 hours postexercise.


CONCLUSIONS
Lack of increase of GLUT-4 gene expression after grain feeding and exercise may explain the apparently slower rate of glycogen synthesis after exercise in horses relative to that of other species.
Jose-Cunilleras
Eduard
E
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA.
Hayes
Kathleen A
KA
Toribio
Ramiro E
RE
Mathes
Lawrence E
LE
Hinchcliff
Kenneth W
KW
D000595:Amino Acid Sequence; D000704:Analysis of Variance; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D016000:Cluster Analysis; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010802:Phylogeny; D010805:Physical Conditioning, Animal; D012333:RNA, Messenger / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
D017931:DNA Primers; D018076:DNA, Complementary; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; D006003:Glycogen