Pharmacological comparison of P2X receptors on rat coeliac, mouse coeliac and mouse pelvic ganglion neurons

Characteristics of P2X receptors on neurons of the rat coeliac, mouse coeli ac and mouse pelvic ganglia have been studied using the whole cell voltage- clamp technique. Fast application of ATP (100 mu M) on to isolated neurons voltage clamped at -70 mV induced a slowly desensitising inward current in 96% of the cells tested. Concentration-response curves far ATP yielded EC50 values of 86 mu M, 64 mu M and 123 mu M, for rat coeliac, mouse coeliac an d mouse pelvic ganglion neurons, respectively, while alpha,beta-methylene A TP was inactive. The response to ATP was antagonised by suramin, Cibacron b lue and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). The potency of ATP was increased by extracellular acidification and by co-appli cation of micromolar concentrations of Zn2+, while raising pH decreased it. On rat coeliac ganglion neurons, the EC50 values for ATP were 35 mu M and 253 mu M at pH 6.8 and 8.0, respectively. On mouse coeliac and pelvic gangl ion neurons, altering the pH produced comparable changes. In conclusion our results indicate that, in contrast to the guinea-pig coeliac ganglion, the characteristics of the P2X receptors present on rat coeliac, mouse coeliac and mouse pelvic ganglia are all identical to those present on rat pelvic ganglion, i.e. they are homomeric P2X(2) receptors, or heteromultimers with P2X, being the dominant subunit. (C) 2000 Elsevier Science Ltd. All rights reserved.