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

Abstract

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), α-amino-3-hydroxy-5methyl-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 ( I KA). (1 S-3 R)1-amino-cyclopentane-1,3-dicarboxylate (1 S-3 R-ACPD) evoked no response. The EC 50 and Hill coefficient ( n H) values of the GluR responses were 3.3×10 −5 M, 0.74 for Glu; 9.0×10 −5 M, 0.83 for NMDA; 6.4×10 −7 M, 1.30 for QA; 1.3×10 −4 M, 1.10 for AMPA and 9.6×10 −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 Ca 2+ permeabilities ( P Ca/ P Cs) of the NMDA and AMPA receptor channels were 8.33 and 1.23, respectively. In addition, the current–voltage ( I– V) relationship of I KA showed little rectification. There was a poor correlation between the Ca 2+ permeability and the shape of the I– V curves of I KA. 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 Ca 2+ permeability but lack of inward rectification). These ionotropic receptor charnels may play important roles in mediating and regulating pelvic visceral information including nociception.