The clustering of neurotransmitter receptors at postsynaptic sites is considered to play an important role in modulating synaptic efficacy. To investigate the mechanisms underlying neurotransmitter receptor clustering, we expressed the NMDA (N-methyl-D-aspartate) receptor NR1A subunit in human embryonic kidney (HEK) 293 cells. As previously shown, the cells exhibited subcellular clusters of the receptor protein with a mean diameter of approximately 0.7 μm. To examine the involvement of cytoskeletal structures on this clustering, we disrupted actin filaments or microtubules by treating the cells with alkaloids. In the actin filament-disrupted cells, the receptor protein shifted from the cellular membrane to the cytoplasm where it formed macroclusters (approximate diameter 3 μm). In the microtubule-disrupted cells, the subcellular clusters of NR1A could not be detected and the protein was diffusely distributed throughout the cytoplasm. Similar results were obtained by coexpression of the receptor protein with fusion proteins harboring various C-terminal exon cassettes. These results suggest that subcellular clustering of the NR1 subunit of the NMDA receptors is regulated by the interaction of its C-terminus with cytoskeletal components, where differentially spliced cassettes interact separately with actin filaments or microtubules. Modulation of the interaction between the neurotransmitter receptors and the cytoskeleton leads to the rearrangement of the receptor clusters and may contribute to certain types of synaptic plasticity. Copyright (C) 1999 Elsevier Science Ireland Ltd.
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