Exercise training does not compensate for age-related decrease in myocardial GLUT-4 content.
We assessed the effects of age and endurance exercise training (treadmill running at 75% maximal running capacity, 1 h/day, 5 days/wk for 10 wk) on the total concentration of insulin-regulatable glucose transporters (GLUT-4) and GLUT-4 mRNA levels in the myocardium of male Fischer 344 rats aged 7, 15, and 25 mo. Myocardial GLUT-4 concentration was quantified with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting and detected with a polyclonal antibody to the GLUT-4 transporter. Myocardial GLUT-4 mRNA levels were quantified with slot-blot analysis and a cDNA probe for GLUT-4. Myocardial GLUT-4 concentration in the 25-mo group decreased 27 and 20% compared with the 7- and 15-mo group, respectively (P < 0.0001 and P < 0.003). GLUT-4 mRNA also decreased significantly in the 25-mo group compared with the 7-mo group (20% in the trained and 11% in the untrained group, P < 0.05). Endurance training did not significantly affect myocardial GLUT-4 concentrations in any age group despite a significant increase in GLUT-4 mRNA in the 7- and 25-mo trained groups. In conclusion, myocardial GLUT-4 protein levels in the rat are significantly decreased with age but are unaffected by 10 wk of treadmill running.
Hall
J L
JL
Institute of Pharmacology, Syntex Discovery Research, Palo Alto, California 94303.
Mazzeo
R S
RS
Podolin
D A
DA
Cartee
G D
GD
Stanley
W C
WC
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D015153:Blotting, Western; D001835:Body Weight / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D051275:Glucose Transporter Type 4; D006019:Glycolysis / Q000502:physiology; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size / Q000502:physiology; D010805:Physical Conditioning, Animal; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011916:Rats, Inbred F344
D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat