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.