Cellular expression of a sodium-dependent monocarboxylate transporter (Slc5a8) and the MCT family in the mouse kidney

Expression analysis of transporters selective for monocarboxylates such as lactate and ketone bodies in the kidney contributes to understanding the renal energy metabolism. Distribution and expression intensity of a sodium-dependent monocarboxylate transporter (SMCT) and proton-coupled monocarboxylate transporters (MCT) were examined in the mouse kidney. In situ hybridization survey detected significant mRNA expressions of SMCT and MCT-1, 2, 5, 8, 9, 10, and 12. Among these, signals for SMCT, MCT2 and MCT8 were predominant; transcripts of SMCT were restricted to the cortex and the outer stripe of outer medulla, while those of MCT2 and MCT8 gathered in the inner stripe of outer medulla and the cortex, respectively. Immunohistochemically, SMCT was present at the brush border in S2 and S3 of proximal tubules, suggesting the active uptake of luminal monocarboxylates here. MCT1 and MCT2 immunoreactivities were respectively found baso-laterally in S1 and thick ascending limbs of Henle's loop. The cellular localization of transporters suggests the involvement of SMCT in the uptake of filtrated lactate and ketone bodies and that of MCTs in the transport of monocarboxylate metabolites between tubular cells and circulation, but the different distribution patterns do not support the notion of a functional linkage between SMCT and MCT1/MCT2.