In recent years it has become apparent that the metabolism of lactate in human skeletal muscle is complex and is regulated by two lactate transporter proteins (MCT1 and MCT4). MCT1 is associated with the influx of lactate into type I muscle fibres. MCT4 is associated with the efflux of lactate out of type II muscle fibres. The purpose of this study was to assess the effects of six-weeks high-intensity interval training on lactate transporter protein and mRNA expression, at rest and 2 hr post exercise. Seven trained endurance runners
(mean ±
sx)
age 28.3 ± 2.9 yr; mass 80.5 ± 5.9 kg;
O2MAX
58.3 ± 2.0 mL.kg-1.min-1) completed a
O2MAX
and a high intensity exhaustive test, before and after a total of 18 sessions of repeated short duration sprints (5-15 s). Muscle biopsies were taken from the vastus lateralis immediately prior and 2 hours post the exhaustive exercise test, pre- and post-training. MCT1 protein increased significantly (P<0.05) over the initial 2 hr post-exercise period (+50%), which was maintained after training (+52%) and increased further (+74%) 2 hr post-exercise. MCT4 protein remained unaltered 2 hr following the initial exercise test and at the completion of the 6 weeks of training. Interestingly, MCT1 mRNA expression decreased significantly (P<0.05) at rest (-49%) after training and 2 hr post-exercise (-54%) after training. Similarly, MCT4 mRNA expression was also decreased significantly (P<0.05) at rest after training (-80%). The data demonstrate selective up-regulation of the lactate transporter isoform MCT1 2 hrs following a high intensity exhaustive test, which remained elevated following interval training. The increases in MCT1 protein occurred despite lowered mRNA abundance, suggesting exercise-mediated increases in translational efficiency and/or protein stability.