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 coeliac and mouse pelvic ganglia have been studied using the whole cell voltage-clamp technique. Fast application of ATP (100 microM) on to isolated neurons voltage clamped at -70 mV induced a slowly desensitising inward current in 96% of the cells tested. Concentration-response curves for ATP yielded EC50 values of 86 microM, 64 microM and 123 microM, for rat coeliac, mouse coeliac and mouse pelvic ganglion neurons, respectively, while alpha,beta-methylene ATP was inactive. The response to ATP was antagonised by suramin, Cibacron blue and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). The potency of ATP was increased by extracellular acidification and by co-application of micromolar concentrations of Zn2+, while raising pH decreased it. On rat coeliac ganglion neurons, the EC50 values for ATP were 35 microM and 253 microM at pH 6.8 and 8.0, respectively. On mouse coeliac and pelvic ganglion 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 P2X2 receptors, or heteromultimers with P2X2 being the dominant subunit.