Detergent Solubilization and Immunoprecipitation of Native NMDA Receptors

Abstract

The N-methyl-d-aspartate (NMDA) subtype of ionotropic glutamate receptor plays a major role in excitatory neurotransmission in the mammalian central nervous system (1,2). It is widely distributed and is found at the postsynaptic membrane of many synapses where it is thought to be anchored to the postsynaptic density (PSD) through a family of PDZ domain-containing proteins (3). Although NMDA receptors are concentrated at the postsynaptic membrane, an intracellular pool, probably representing receptors being transported to and from the synapse, is also present (4,5). Molecular cloning studies have identified five subunits, NR1 and NR2A-D, which can assemble and form functional receptor complexes in oocytes or transfected cell expression systems (2). The receptor complex is believed to be either a tetramer or pentamer comprised of NR1 and NR2 subunits (6,7). The number and composition of subunits in native receptors remain uncertain, but in expression systems, NR1 subunits are required for a functional receptor. Eight different splice variants of NR1, with distinct functional properties, have been identified (2). The NR2 subunits and NR1 splice variants are differentially distributed in the central nervous system indicating that a wide range of functionally distinct receptor complexes may be selectively expressed in different brain regions and neuronal cell types. The nature of these complexes can be explored with antibodies selective for the different forms of the receptor (4–6).