The effect of transient global ischemia on the interaction of Src and Fyn with the N-methyl-D-aspartate receptor and postsynaptic densities: Possibleinvolvement of Src homology 2 domains

Transient ischemia increases tyrosine phosphorylation of N-methyl-D-asparta te (NMDA) receptor subunits NR2A and NR2B in the rat hippocampus. The autho rs investigated the effects of this increase on the ability of the receptor subunits to bind to the Src homology 2 (SH2) domains of Src and Fyn expres sed as glutathione-S-transferases-SH2, fusion proteins. The NR2A and NR2B b ound to each of the SH2 domains and binding was increased approximately two fold after ischemia and reperfusion. Binding was prevented by prior incubat ion of hippocampal homogenates with a protein tyrosine phosphatase or by a competing peptide for the Src SH2 domain. Ischemia induced a marked increas e in the tyrosine phosphorylation of several proteins in the postsynaptic d ensity (PSD), including NR2A and NR2B, but had no effect on the amounts of individual NMDA receptor subunits in the PSD. The level of Src and Fyn in P SDs, but not in other subcellular fractions, was increased after ischemia. The ischemia-induced increase in the interaction of NR2A and NR2B with the SH2 domains of Src and Fyn suggests a possible mechanism for the recruitmen t of signaling proteins to the PSD and may contribute to altered signal tra nsduction in the postischemic hippocampus.