Acute Exercise And Monocarboxylate Transporter (mct)1 And Mct4 In Thoroughbred Horses

Abstract

MCT (monocarboxylate transporter) 1 and MCT4 are known as the key lactate transporters in skeletal muscle. As a part of lactate shuttle, MCT1 facilitates uptake of lactate, while MCT4 facilitates lactate extrusion. Thoroughbred horses are athletes with a high capacity for exercise. They have exceptionally high maximal oxygen uptake, and a high amount of energy stored as glycogen in the muscles. Blood lactate concentration reaches 30 - 40 mmol during exercise. Although it is suggested that MCT1 and MCT4 play an important role during exercise in horses, it is still not known that whether acute exercise can increase MCT1 and MCT4 protein content in horses. PURPOSE: To investigate effects of acute exercise on MCT1, MCT4 and lactate metabolism in Thoroughbreds muscle. METHODS: Six Thoroughbred horses (3-4 years old; 3 males and 3 females) were given an incremental exercise test (IET). The speed of treadmill was increased by 2 m/s every minute from 6 m/s until the horse could not maintain its position on the treadmill from exhaustion. Blood samples are taken during IET. Muscle samples were obtained from the middle gluteus muscle before and after 0, 3, 6, and 24 hours from IET. Protein contents of MCT1 and MCT4 were measured by Western blotting. RESULTS: The average VO2max was 168.5 ± 4.4 ml/kg/min. Peak running speed was 13.3 ± 0.4 m/s. Plasma lactate concentration at exhaustion was 23.2 ± 3.0 mmol. The protein contents of MCT1 and MCT4 were increased after 6 hours from IET (+19 and +34% vs PRE, respectively; P<0.05) and returned to the pre-training value after 24 hours. Muscle glycogen concentration was decreased after IET (-50% vs PRE, P<0.01) and remained decreased after 3 and 6 hours (-30% and -19% vs PRE, respectively; P<0.05), and returned to the pre-training value after 24 hours from IET. CONCLUSIONS: This study showed that MCT1 and MCT4 proteins can be increased by acute exercise. Therefore, MCT1 and MCT4 might belong to genes that are very rapidly up-regulated with an exercise stimulus.