Effects of transient global ischemia on distribution and phosphorylation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors at the synapse

alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are implicated in ischemia-induced neuronal death. We investigated the effects of global ischemia on distribution and phosphorylation of synaptic AMPARs in lipid rafts (DRMs), post-synaptic densities (PSDs) and extra-synaptic membranes (detergent soluble fraction) at various recovery times. We determined that 0.5% Triton X-100 (TX-100) with 1:1 detergent to protein ratio was the preferred condition to isolate post-synaptic DRMs. After ischemia, following an initial decrease there was a trend towards increase in synaptic AMPARs by 24 hours. AMPARs increased in PSDs at 6 hours in forebrain and hippocampus. GluR1 phosphorylation at Ser-831 decreased in DRMs and PSDs at 24 hours. Ser-845 showed increase in PSDs and transient changes in DRM and soluble fractions. Increased synaptic GluR1 is consistent with increased Ser-845 phosphorylation. The findings suggest that different synaptic populations of AMPARs are regulated differently after ischemia and lipid rafts may be involved in regulating AMPAR distribution.