Effects of Training on Monocarboxylate Transporters (MCT1, MCT2 and MCT4) in Vastus Lateralis Muscle from Standardbred Horses

During intense exercise, lactic-acid accumulates in skeletal muscle and protons build up which causes a decrease in pH and leads to inhibition of muscle function and eventually fatigue. A family of Monocarboxylate Transporters (MCTs) have been identified in equine skeletal muscle but its function during training has not yet been fully elucidated. We hypothesize an important function of MCT1, 2 and 4 in equine muscle. Six Standardbred geldings were trained for a total of 22 weeks in 2 phases (endurance phase and high intensity phase). Exercise intensity during the training sessions were based on fixed percentages of the peak heart frequency (HRpeak) determined during a Standard Exercise Test (SET). At the beginning and end of each phase a SET was performed. Venous blood was drawn from the jugular vein before the test (t=0 minutes), after the warming up (t=9 minutes), and every 5 minutes during the SET (t=14, 19, 24, 29, 34). Samples were kept on ice until whole blood lactic acid had been analysed. Muscle biopsies were taken approximately 60 minutes before each SET using a modified Bergström biopsy needle. Blood and fat tissue were removed from the biopsy and the biopsy was there after immediately frozen in liquid nitrogen for biochemical analysis and Western-blotting for MCT expression