Expression of the monocarboxylate transporter MCT2 by rat brain glia

The nucleotide sequence of the rat monocarboxylate transporter MCT2 was determined from brain-derived cDNA. A polyclonal antibody was raised in chickens against the carboxyl terminal end of the deduced amino acid sequence and affinity purified. The MCT2 antibody identified a 46-kDa band on immunoblots and labeled kidney, skeletal muscle, and stomach consistent with the reported cellular expression for this transporter. Light microscopic immunocytochemistry indicated that the MCT2 transporter was abundant in glial limiting membranes, ependymocytes, and neuropil, particularly in the lacunosum molecular layer of hippocampus and the molecular layer of cerebellum. Labeled astrocytes were commonly observed in white matter. The distribution of this transporter differed in several respects from that previously reported for MCT1. MCT2 was abundantly distributed in astrocyte foot processes and was usually not detected in other cells of the cerebrovasculature, including vascular smooth muscle cells, pericytes, and endothelium. In addition, the granular layer of cerebellum, which showed little MCT1 labeling, exhibited MCT2 labeling of cellular processes in the neuropil surrounding the granule and Purkinje cells. The results lend support to the concept that astrocytes play a significant role in cerebral energy metabolism by transporting lactate and other monocarboxylates.