Ontogeny and localization of the neutral amino acid transporter ASCT1 in rat brain

ASCT1 is a protein that encodes System ASC, a sodium-dependent amino acid t ransport activity that transports primarily zwitterionic amino acids at phy siological pH. ASCT1 has a 39-44% identity to the EAAT family of glutamate transporters. At extracellular pH values below 7.4, ASCT1 shifts substrate specificity to transport anionic amino acids. In this study We have examine d the location of the ASM transporter by immunohistochemistry in the develo ping rat brain. In addition, we have examined the cellular localization of ASCT1 in glial and neuronal cultures. The presence of ASCT1 immunoreactivit y (ASCTlir) in the developing brain was detectable as early as 14 days of g estation. At the cellular level, ASCTlir was prominent in hippocampal pyram idal and dentate granule neurons. In the cerebellum, Purkinje cells and the ir dendrites were intensely labeled, whereas the granule and molecular laye rs were moderately labeled. In the cerebral cortex, neuronal cell bodies in all lamina and scattered astrocytes showed intense ASCTlir. Double labelin g experiments in vitro confirmed that ASCT1 was localized to both glia and neurons. These data illustrate that the rat ASCT1 transporter is expressed in the developing brain at levels equivalent to those observed in adult tis sue. In addition, the expression and localization of ASCT1 are consistent w ith its possible role in pathophysiological processes that involve glutamat e toxicity. (C) 2001 Elsevier Science B.V. All rights reserved.