Localization of members of MCT monocarboxylate transporter family Slc16 in the kidney and regulation during metabolic acidosis.

The monocarboxylate transporter family (MCT) comprises 14 members with distinct transport properties and tissue distribution. The kidney expresses several members of the MCT family, but only little is known about their exact distribution and function. Here, we investigated selected members of the MCT family in the mouse kidney. MCT1, MCT2, MCT7, and MCT8 localized to basolateral membranes of the epithelial cells lining the nephron. MCT1 and MCT8 were detected in proximal tubule cells whereas MCT7 and MCT2 were located in the thick ascending limb and the distal tubule. CD147, a beta-subunit of MCT1 and MCT4, showed partially overlapping expression with MCT1 and MCT2. However, CD147 was also found in intercalated cells. We also detected SMCT1 and SMCT2, two Na(+)-dependent monocarboxylate cotransporters, on the luminal membrane of type A intercalated cells. Moreover, mice were given an acid load for 2 and 7 days. Acidotic animals showed a marked but transient increase in urinary lactate excretion. During acidosis, a downregulation of MCT1, MCT8, and SMCT2 was observed at the mRNA level, whereas MCT7 and SMCT1 showed increased mRNA abundance. Only MCT7 showed lower protein abundance whereas all other transporters remained unchanged. In summary, we describe for the first time the localization of various MCT transporters in mammalian kidney and demonstrate that metabolic acidosis induces a transient increase in urinary lactate excretion paralleled by lower MCT7 protein expression.