AMPA receptor protein expression and function in astrocytes cultured from hippocampus

Glutamate receptors guide the proliferation, migration, and differentiation of glial cells. Here, we characterize AMPA (alpha-amino-3-hydroxy-5-methyl -4-isoxazole-propionic acid) and NMDA receptor protein expression and funct ion and mRNA expression in hippocampal glial cultures. By immunocytochemist ry, GluR2 (the subunit that limits the Ca2+ permeability of AMPA receptors) exhibited prominent labeling in hippocampal glial cultures. Double-labelin g of GluR2 with GFAP and with A2B5 revealed GluR2 subunit expression on typ e-1 and type-2 astrocyte lineage cells. GluR1 subunit expression was more p rominent in type-1 than in type-2 astrocytes. To characterize functional pr operties of glutamate receptors expressed in cultured hippocampal astrocyte s, we performed whole-cell patch clamp recording. Application of L-glutamat e, AMPA, and kainate, but not NMDA, to small, rounded cells (morphologicall y identified as type-2 astrocytes) elicited inward currents which were bloc ked by the AMPA/kainate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CN QX), Cyclothiazide potentiated AMPA- and kainate-elicited currents, indicat ive of AMPA-preferring receptors, Current voltage analysis indicated that t ype-2 astrocyte AMPA receptors were electrically linear, indicative of GluR 2-containing, Ca2+-impermeable AMPA receptors, By Northern blot analysis, G luR1 mRNA was highest in astrocyte cultures from cerebellum and hippocampus and moderate in astrocyte cultures from neocortex and striatum, GluR3 mRNA was detectable in astrocyte cultures from cerebellum and neocortex, GluR2 and NR1 mRNA expression were not detected in astrocytes cultured from any b rain region examined. In situ hybridization studies showed wide expression of GluR1 mRNA in cultured astrocytes; GluR2 and GluR3 mRNAs were near backg round levels. Thus, cultured type-2 astrocytes express functional AMPA rece ptors in a cell-specific and region-specific manner, consistent with their role in neuronal-glial communication. (C) 1999 Wiley-Liss, Inc.