PRESENCE OF N-METHYL-D-ASPARTATE (NMDA) RECEPTORS IN NEUROBLASTOMA X GLIOMA HYBRID NG108-15 CELLS-ANALYSIS USING [CA-45(2+)]INFLUX AND [H-3] MK-801 BINDING AS FUNCTIONAL MEASURES

In the present study, we have attempted to clarify whether neuroblastoma glioma hybrid NG 108-15 cells (NG cells) possess the NMDA receptor complex using [Ca-45(2+)]influx and [H-3]MK-801 binding as functional measures. Glutamate and NMDA dose-dependently increased [Ca-45(2+)]influx and these increases were further enhanced by glycine. Scatchard analysis revealed the presence of a high-affinity binding site for [H-3]MK-801 with a K-D of 18.8 nM and a B-max of 0.328 pmol/mg protein. This [H-3]MK-801 binding was also increased by NMDA in a dose-dependent manner and this increase was further enhanced by glycine. Both ketamine and MK-8O1 inhibited glutamate- and NMDA-induced [Ca-45(2+)]influx as well as the increase of [3H]MK-801 binding in a dose-dependent manner. Similarly, Mg2+ and Zn2+ dose-dependently reduced both glutamate-induced [Ca-45(2+)]influx and [H-3]MK-801 binding. Spermine, one of the polyamines, showed a biphasic stimulatory effects on glutamate-induced [Ca-45(2+)]influx and [3H]MK-801 binding. These results indicate that NG cells possess a pharmacologically distinct NMDA receptor complex and suggest that these cells may be useful for the analyses on pharmacological and biochemical characteristics of the NMDA receptor complex.