CALCIUM-ENTRY THROUGH A SUBPOPULATION OF AMPA RECEPTORS DESENSITIZED NEIGHBORING NMDA RECEPTORS IN RAT DORSAL HORN NEURONS

1. A Ca2+-dependent interaction between non-NMDA and NMDA receptors wa s studied in embryonic rat dorsal horn neurons grown in tissue culture using perforated-patch recording. Specifically, non-NMDA receptors we re found to induce reversible inhibition of NMDA receptors in a manner dependent on the presence of extracellular Ca2+. 2. Non-NMDA receptor -induced inhibition of NMDA receptors was mediated by the elevation of intracellular Ca2+ concentration produced by Ca2+ entry through a sub population of pha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA ) non-NMDA receptors. Furthermore, Ca2+ entry through the AMPA channel s alone is sufficient for desensitization of NMDA channels to occur. 3 . Imaging of neuritic sites of Ca2+ entry revealed that Ca2+-permeable AMPA channels are often co-localized with NMDA channels on dorsal hor n neurons, indicating that the Ca2+ mediated interaction between recep tors may occur within small dendritic domains. 4. The ability of Ca2+- permeable AMPA channels to inhibit adjacent NMDA channels may contribu te to the postsynaptic integration of excitatory input.