SAP97 concentrates at the postsynaptic density in cerebral cortex

SAP97, a PDZ-containing protein, is reported to concentrate in axon termina ls, where its function remains unknown. Using highly specific new antibodie s, we show that SAP97 in rat cerebral cortex is associated with heteromeric AMPA receptors via a selective biochemical interaction between SAP97 and t he GluR1 subunit. Using light and electron microscopic immunocytochemistry, we demonstrate cellular and synaptic colocalization of SAP97 and GluR1, an d show that SAP97 concentrates at synapses that contain GluR1 but not neces sarily GluR2 or GluR3. Using quantitative postembedding immunogold electron microscopy, we find that SAP97 is at highest concentration within the post synaptic density of asymmetric synapses. These data suggest that SAP97 may help to anchor GluR1-containing AMPA receptors at the synapse. As a multifu nctional scaffolding protein, SAP97 may organize components of AMPA-related intracellular signalling pathways, including those associated with calcium -permeable homomeric GluR1 channels.