Immunoreactivity of receptor and transporters for lactate located in astrocytes and epithelial cells of choroid plexus of human brain.

Glucose metabolism produces lactate and hydrogen ions in an anaerobic environment. Cerebral ischemia or hypoxia is believed to become progressively lactacidemic. Monocarboxylate transporters (MCTs) in endothelial cells are essential for the transport of lactate from the blood into the brain. In addition, it is considered that MCTs located in astrocytic and neuronal cells play a key role in the shuttling of energy metabolites between neurons and astrocytes. However, roles of lactate in the brain remain to be clarified. In this study, the localization of lactate transporters and a receptor for cellular uptake of lactate was immunohistochemically examined in autopsied human brains. Immunoreactivity for MCT1 was observed in the apical cytoplasmic membrane of some epithelial cells in the choroid plexus as well as astrocytes and the capillary wall, whereas that for MCT4 was found in the basolateral cytoplasmic membrane of small number of epithelial cells as well as astrocytes and the capillary wall. In addition, immunoreactivity for the hydroxy-carboxylic acid 1 receptor (HCA1 receptor), a receptor for cellular uptake of lactate, was also found on the basolateral cytoplasmic membrane of epithelial cells as well as astrocytic and neuronal cells. Immunoreactivity for lactate dehydrogenase (LDH)-B was observed in the cytoplasm of epithelial cells in the choroid plexus as well as astrocytes and the capillary wall. These immunohistochemical findings indicate the localization of MCT1, MCT4, the HCA1 receptor, and LDH-B in epithelial cells of the choroid plexus as well as astrocytes, and suggest the transport of intravascular lactate into the brain through epithelial cells of the choroid plexus as well as cerebral vessels and the possibility of lactate being utilized in epithelial cells.