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

Nystatin perforated patch and conventional whole-cell recording configurations were used to characterize the properties of ionotropic glutamate receptor (GluR) channels in neurons freshly dissociated from the rat sacral dorsal commissural nucleus (SDCN). L-Glutamate (Glu), N-methyl-D-aspartate (NMDA), quisqualate (QA), alpha-amino-3-hydroxy-5-methyl-4-isoxazoleprop ionate (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 (IKA). (1S-3R)1-amino-cyclopentane-1,3-dicarboxylate (1S-3R-ACPD) evoked no response. The EC50 and Hill coefficient (nH) 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 all 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 potentiated 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 reversibly blocked both the currents. The Ca2+ permeabilities (PCa/PCs) of the NMDA and AMPA receptor channels were 8.33 and 1.23, respectively. In addition, the current-voltage (I-V) relationship of IKA showed little rectification. There was a poor correlation between the Ca2+ permeability and the shape of the I-V curves of IKA. These results suggest that rat SDCN neurons possess NMDA and non-NMDA receptor channels, and express AMPA type receptors with unique properties (slow desensitization to AMPA, high Ca2+ permeability but lack of inward rectification). These ionotropic receptor channels may play important roles in mediating and regulating pelvic visceral information including nociception.