Functional properties of ionotropic glutamate receptor channels in rat sacral dorsal commissural neurons

Nystatin perforated patch and conventional whole-cell recording configurati ons were used to characterize the properties of ionotropic glutamate recept or (GluR) channels in neurons freshly dissociated from the rat sacral dorsa l commissural nucleus (SDCN). L-Glutamate (Glu), N-methyl-D-aspartate (NMDA ), quisqualate (QA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate ( AMPA) and kainate (KA) applied via a Y-tube produced inward currents at -44 mV which increased in a concentration-dependent manner; they desensitized when induced at higher concentrations except for the KA-induced current (I- KA). (1S-3R)1-amino-cyclopentane-1,3-dicarboxylate (1S-3R-ACPD) evoked no r esponse. The EC50 and Hill coefficient (n(H)) values of the GluR responses were 3.3 x 10(-5) M, 0.74 for Glu; 9.0 x 10(-5) M, 0.83 for NMDA; 6.4 x 10( -7) M, 1.30 for QA; 1.3 x 10(-4) M, 1.10 for AMPA and 9.6 x 10(-5) M. 1.30 for KA, respectively. The reversal potentials of the GluR responses were al l near 0 mV. The 6-Cyano-7-nitroquinoxaline-2-3-dione (CNQX) and D-2-amino- 5-phosphonovalerate (D-APV) suppressed the non-NMDA and NMDA responses in a concentration-dependent manner, respectively. Cyclothiazide strongly poten tiated both KA- and AMPA-induced responses while concanavalin A potentiated both the responses to a much lesser degree. NS-102 produced no significant effect on either KA- or AMPA-activated currents, while GYKI 52466 reversib ly blocked both the currents. The Ca2+ permeabilities (P-Ca/P-Cs) of the NM DA and AMPA receptor channels were 8.33 and 1.23, respectively. Tn addition , the current-voltage (I-V) relationship of I-KA showed little rectificatio n. There was a poor correlation between the Ca2+ permeability and the shape of the I-V curves of I,. These results suggest that rat SDCN neurons posse ss NMDA and non-NMDA receptor channels, and express AMPA type receptors wit h unique properties (slow desensitization to AMPA, high Ca2+ permeability b ut lack of inward rectification). These ionotropic receptor charnels may pl ay important roles in mediating and regulating pelvic visceral information including nociception. (C) 1999 Elsevier Science Ltd. All rights reserved.