Abstract
The N-methyl-D-aspartate (NMDA) subtype of ionotropic glutamate receptor is assembled from one NR1 subunit, expressed in eight splice variants, and four NR2 subunits (NR2A-D). The combination of subunits and splice variants determines the pharmacological and physiological properties of the receptor. In the present study we investigated the relationship between NR1 splice variants and NR2 subunits in rat brain using a series of antibodies selective for the four NR1 cassettes, which vary in the NR1 splice variants, and for NR2A and NR2B. Sodium deoxycholate at pH 9.0 solubilized about 35% of the receptor, which was intact based on co-immunoprecipitation of NR1 and NR2 subunits and chemical cross-linking of the solubilized receptor. The cross-linked product contained three high molecular weight components, Mr = 603,000, 700,000, and 750,000, which were immunolabeled with antibodies to NR1 and to NR2 subunits. Immunoprecipitation analyses using antibodies selective for NR2A and NR2B showed no preferential assembly between NR2 subunits and NR1 splice variants. There was little co-immunoprecipitation of NR2A and NR2B, suggesting that most NMDA receptor complexes contain only one of these subunits. However, receptor complexes can contain at least two different NR1 splice variants. In developing conditions for the solubilization of intact NMDA receptor complexes, we observed a differential solubilization of NR1 and NR2 subunits. NR2 was nearly insoluble in Triton X-100 in both microsomal and synaptic membrane fractions, while NR1 was readily soluble in the microsomal fraction but insoluble in the synaptic membrane fraction. These results suggest that the NR1 subunit is modified when it is incorporated into the synaptic membrane, possibly by strengthening its interaction with NR2 or another synaptic protein.
Highlights
In vitro expression studies show that receptor complexes made up of different NR1 splice variants and NR2 subunits have distinct pharmacological and physiological properties [2, 11, 13, 20, 21]
Variants containing the C1 cassette formed receptor-rich aggregates on the plasma membrane when exThe N-methyl-D-aspartate (NMDA)1 subtype of ionotropic pressed in cultured fibroblasts; splice variants lacking this glutamate receptor plays a central role in excitatory neuro- domain were distributed throughout the cytoplasm [35]
Tibodies selective for the N1 and C1 cassettes, Sheng et al [37] suggested that certain splice variants may be selectively associated with different NR2 subunits. These findings suggest NMDA receptor complexes may be selectively targeted to, and stabilized at, postsynaptic locations based on particular splice variants of NR1 present in the complex, and that the NR2 subunits present in the complex may be related to the NR1 splice variants
Summary
Vol 271, No 26, Issue of June 28, pp. 15669 –15674, 1996 Printed in U.S.A. Relationship between N-Methyl-D-aspartate Receptor NR1 Splice Variants and NR2 Subunits*. There was little co-immunoprecipitation of NR2A and NR2B, suggesting that most NMDA receptor complexes contain only one of these subunits. In vitro expression studies show that receptor complexes made up of different NR1 splice variants and NR2 subunits have distinct pharmacological and physiological properties [2, 11, 13, 20, 21]. Multiple NMDA receptor complexes, with different splice variant and subunit compositions, may be present in a neuron with only some destined for synaptic expression. Such an interpretation would be consistent with the relatively large intracellular pool of receptor seen for most.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
