Fig. 4.

Succinate is transported by MCT1 as the monocarboxylate anion.

MCT1 was expressed in Xenopus laevis oocytes proton-linked monocarboxylate transport measured in real time using the pH-sensitive fluorescent dye BCECF as described previously [100]. Panel A shows that 30 mmol/L l-lactate (L) is transported into and out of Xenopus laevis oocytes expressing MCT1 at both pH 7.4 and 6.0 but not control oocytes. By contrast, 30 mmol/L succinate (S) is only transported after the external pH has been decreased to 6.0 consistent with its transport as a monocarboxylate (i.e. in the monoprotonated form). Panel B shows that transport of both succinate and l-lactate at pH 6.0 is blocked by prior exposure of the oocyte to 1 μmol/L AR-C155858, a specific MCT1 inhibitor [100].