Glycine-insensitive NMDA-sensitive receptor expressed in Xenopus oocytes by guinea pig cerebellar mRNA

The electrophysiological and pharmacological properties of N-methyl-D-aspartate (NMDA)-sensitive receptors expressed in Xenopus oocytes by injection of total poly(A)+RNAs (mRNAs) from the cerebellum and cerebrum of guinea pigs were compared. The inward current induced by NMDA under voltage-clamp in cerebellar mRNA-injected oocytes was depressed in a voltage-dependent fashion by Mg2+ to show a negative slope conductance and selectively antagonized by D-2-amino-5-phosphonovalerate (D-APV) and phencyclidine (PCP). Glycine (0.01-10 microM) did not potentiate NMDA-induced currents in cerebellar mRNA-injected oocytes, while it potentiated NMDA-induced currents in cerebral mRNA-injected oocytes in a dose-dependent fashion. 6-Cyano-7-nitroquinoxaline-2,3-dione and 7-chlorokynure-nate suppressed the NMDA response but significantly less potently in cerebellar mRNA-injected oocytes than in cerebral mRNA-injected oocytes. These results suggest that the NMDA-sensitive receptor expressed in Xenopus oocytes by guinea pig cerebellar mRNA resembles the cerebral NMDA receptor in its high sensitivities to Mg2+, PCP, and D-APV, but it is distinct from the cerebral NMDA receptor in responsiveness to glycine.