Isoform-specific regulation of the lactate transporters MCT1 and MCT4 by contractile activity

We examined the isoform-specific regulation of monocarboxylate transporter (MCT)1 and MCT4 expression by contractile activity in red and white tibiali s anterior muscles. After 1 and 3 wk of chronic muscle stimulation (24 h/da y), MCT1 protein expression was increased in the red muscles (+78%, P < 0.0 5). In the white muscles, MCT1 was increased after 1 wk (+191%) and then wa s decreased after 3 wk. In the red muscle, MCT1 mRNA accumulation was incre ased only after 3 wk (+21%; P < 0.05). In the white muscle, MCT1 mRNA was i ncreased after 1 wk (+30%; P < 0.05) and 3 wk (+15%; P < 0.05). MCT4 protei n was not altered in either the red or white muscles after 1 or 3 wk. MCT4 mRNA was transiently lowered (similar to 15%) in both muscles in the 1st wk , but MCT4 mRNA levels were back to control levels after 3 wk. In conclusio n, chronic contractile activity induces the expression of MCT1 but not MCT4 . This increase in MCT1 alone was sufficient to increase lactate uptake fro m the circulation.