Distinct distributions of alpha-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 known alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunits (GluR1-4) were used to screen regional homogenates and subcellular fractions From rat brain. Affinity purified anticholera (against amino acids 877-889), anti-GluR2/3 (850-862), and anti-GluR4a and anti-GluR4b (868-881) labeled distinct subunits with the expected molecular weight of similar to 105,000. These anligens were shown to have distinct distributions in the brain. While GluR2/3 epitopes had a distribution profile similar to that ofthe presynaptic marker synaptophysin, GluR1 was notable for its abundance in the hippocampus and its relatively low density in neocortical areas, and GluR4 was highly enriched in cerebellar tissue. An additional antigen (glutamate receptor-related, GR53) of lower molecular weight (50,000-59,000) was reconnized in rat, human, frog, chick and goidfish brain samples by anti-GluR4a as well as by anti-GluR1at, an antibody that specifically recoonizes the extracellular aminolerminal domain of GluR1 (amino acids 163-188). Both antibodies also labeled antigens of similar to 105,000 mol. wt in brain tissue from all species tested. The similar to 53,000 mol. wt antigen was concentrated 10-20-fold in synaptic membranes vs homogenates across rat brain regions. Both the 105,000 and the 53,000 mel. wt proteins were also concentrated in postsynaptic densities, and neither of the two antigens were evident in seven non-brain tissue samples. These data indicate that AMPA recrptors have regionally different subunit combinations and that some AiLIPA receptor composites include proteins other than the conventional 105,000 mel. wt GluR subunits. Copyright (C) 1996 IBRO.