Characterization of desensitization in recombinant N-methyl-D-aspartate receptors:: comparison with native receptors in cultured hippocampal neurons

In the present study we have characterized the effect of Ca2+, glycine, and agonist concentration on inactivation and desensitization in native and recombinant N-methyl-D-aspartate (NMDA) receptors. In agreement with earlier studies on neurons, we found that in the presence of saturating glycine concentrations, lowering [Ca2+](o), will decrease inactivation of NMDA receptors in cultured hippocampal neurons. However, unlike native NMDA receptors under the same recording conditions, recombinant receptors did not exhibit Ca2+-dependent inactivation. We also show that the glycine-insensitive desensitization observed in the recombinant receptors is subunit dependent, as NR1a2A and NR1a2B receptors significantly desensitized while the NR1a2C combination hid not. Furthermore, we show this form of desensitization in NR1a2A receptors is due to classic agonist-induced desensitization. In addition, we demonstrate the presence of glycine-dependent desensitization in recombinant receptors. The ability of glycine to inhibit desensitization correlates to the rank order of glycine's affinity for potentiating the peak response for each subtype. Finally, using ifenprodil in the presence of high and low glycine concentrations, we present evidence that both 2A-like and 2B-like subtypes of receptors can independently coexist in single neurons. (C) 1998 Elsevier Science B.V. All rights reserved.