DISTINCT DISTRIBUTIONS OF PHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONATE (AMPA) RECEPTOR SUBUNITS AND A RELATED 53,000 M(R) ANTIGEN (GR53) IN BRAIN-TISSUE

Polyclonal antibodies against specific carboxy-terminal sequences of k nown pha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) recepto r subunits (GluR1-4) were used to screen regional homogenates and subc ellular fractions From rat brain. Affinity purified anticholera (again st amino acids 877-889), anti-GluR2/3 (850-862), and anti-GluR4a and a nti-GluR4b (868-881) labeled distinct subunits with the expected molec ular weight of similar to 105,000. These anligens were shown to have d istinct distributions in the brain. While GluR2/3 epitopes had a distr ibution profile similar to that ofthe presynaptic marker synaptophysin , GluR1 was notable for its abundance in the hippocampus and its relat ively low density in neocortical areas, and GluR4 was highly enriched in cerebellar tissue. An additional antigen (glutamate receptor-relate d, GR53) of lower molecular weight (50,000-59,000) was reconnized in r at, human, frog, chick and goidfish brain samples by anti-GluR4a as we ll as by anti-GluR1at, an antibody that specifically recoonizes the ex tracellular aminolerminal domain of GluR1 (amino acids 163-188). Both antibodies also labeled antigens of similar to 105,000 mol. wt in brai n tissue from all species tested. The similar to 53,000 mol. wt antige n was concentrated 10-20-fold in synaptic membranes vs homogenates acr oss rat brain regions. Both the 105,000 and the 53,000 mel. wt protein s were also concentrated in postsynaptic densities, and neither of the two antigens were evident in seven non-brain tissue samples. These da ta indicate that AMPA recrptors have regionally different subunit comb inations and that some AiLIPA receptor composites include proteins oth er than the conventional 105,000 mel. wt GluR subunits. Copyright (C) 1996 IBRO.