PHARMACOLOGICAL AND MOLECULAR CHARACTERIZATION OF P2X RECEPTORS IN RAT PELVIC GANGLION NEURONS

1 The presence and characteristics of P2X receptors on neurons of the rat major pelvic ganglia (MPG) have been studied using whole cell volt age-clamp, in situ hybridization and immunohistochemistry. 2 Rapid app lication of ATP (100 mu M) to isolated rat MPG neurons induced moderat ely large inward currents (0.33-5.3 nA) in 39% of cells (108/277). The response to ATP occurred very rapidly, with an increase in membrane c onductance, and desensitized slowly. 3 The concentration-response curv e for ATP yielded an EC50 of 58.9 mu M. The agonist profile was ATP gr eater than or equal to 2MeSATP = ATP gamma S > BzATP, while alpha,beta -MeATP, beta,gamma-MeATP, UTP and ADP were all inactive at concentrati ons up to 100 mu M. 4 The response to ATP was antagonized by suramin ( pA(2) = 5.6), reactive blue-2 (IC50 = 0.7 mu M) and pyridoxalphosphate -6-azophenyl-2',4'-disulphonic acid (PPADS). 5 Lowering the pH from 7. 4 to 6.8 produced a marked potentiation (to 339% of control) of the re sponses to ATP (30 mu M), while raising the pH to 8.0 attenuated the r esponses (to 20% of control). The EC(50)s for ATP were 28.8, 58.9 and 264 mu M at pH 6.8, 7.4 and 8.0, respectively. 6 Co-application of ATP with Zn2+ produced a marked enhancement of the responses to ATP, with an EC50 of 9.55 mu M. In the presence of Zn2+ (30 mu M), the EC50 for ATP was decreased to 4.57 mu M. 7 In situ hybridization revealed that the P2X receptor transcripts levels in rat MPG neurons are P2X(2) > P 2X(4) > P2X(1), P2X(3), P2X(5) and P2X(6). The immunohistochemical sta ining revealed a small number of neurons with strong P2X(2) immunoreac tivity. 8 In conclusion, our results indicate that there are P2X recep tors present on MPG neurons. The pharmacological characteristics of th ese receptors, the in situ hybridization and immunohistochemical evide nce are consistent with them being of the P2X(2) subtype, or heteromul timers, with P2X(2) being the dominant component.