title: Conditioning increases the gain of contraction-induced sarcolemmal substrate transport in ultra-endurance racing sled dogs.
abstract: Endurance exercise relies on transsarcolemmal flux of substrates in order to avoid depletion of intramuscular reserves. Previous studies of endurance trained sled dogs have shown a remarkable capacity of these dogs to adapt rapidly to endurance exercise by decreasing the utilization of intramuscular reserves. The current study tested the hypothesis that the dogs' glycogen-sparing phenotype is due to increased sarcolemmal transport of glucose and fatty acids. Basal and exercise-induced transport of glucose and fatty acids into sarcolemmal vesicles was evaluated in racing sled dogs prior to and after 7 months of exercise conditioning. Sarcolemmal substrate transport capacity was measured using sarcolemmal vesicles and radiolabelled substrates, and transporter abundance was measured using Western blot quantification in whole muscle homogenates and the sarcolemmal vesicle preparations. Conditioning resulted in increased basal and exercise-induced transport of both glucose and palmitate. Neither acute exercise nor conditioning resulted in changes in muscle content of GLUT4 or FAT/CD36, but conditioning did result in decreased abundance of both transporters in the sarcolemmal vesicles used for the basal transport assays, and this decrease was further amplified in the vesicles used for the exercise-induced transport assays. These results demonstrate conditioning-induced increases in sarcolemmal transport of oxidizable substrates, as well as increased gain of exercise-induced sarcolemmal transport of these substrates. These results further indicate that increased sarcolemmal transport of oxidizable substrates may be due to either an increased intrinsic capacity of the existing transporters or to a different population of transporters from those investigated.
authors: Department of Physiological Sciences, Oklahoma State University, Stillwater, Oklahoma, United States of America.
authors: Michael S
authors: MS
authors: Davis
authors: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors: Arend
authors: A
authors: Bonen
authors: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors: Laelie A
authors: LA
authors: Snook
authors: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors: Swati S
authors: SS
authors: Jain
authors: Department of Veterinary Clinical Sciences, Oklahoma State University, Stillwater, Oklahoma, United States of America.
authors: Kenneth
authors: K
authors: Bartels
authors: Department of Large Animal Clinical Science, Michigan State University, East Lansing, Michigan, United States of America.
authors: Raymond
authors: R
authors: Geor
authors: Department of Veterinary Medicine, University of Alaska-Fairbanks, Fairbanks, Alaska, United States of America.
authors: Karsten
authors: K
authors: Hueffer
mesh_terms: D000818:Animals; D001692:Biological Transport; D018955:CD36 Antigens / Q000378:metabolism; D004285:Dogs; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000378:metabolism; D010168:Palmitates / Q000378:metabolism; D010805:Physical Conditioning, Animal; D010807:Physical Endurance; D012508:Sarcolemma / Q000378:metabolism*
chemical_list: D018955:CD36 Antigens; D051275:Glucose Transporter Type 4; D009124:Muscle Proteins; D010168:Palmitates; D005947:Glucose