Evidence for the presence of P2y and P2x receptors with different functions in mouse stomach

To clarify the function of P2 receptor subtypes in mouse stomach, the motor responses to ATP, a,h-methyleneATP (a,h-MeATP), P2Xreceptor agonist, 2-methylthioATP (2-MeSATP), P2Y receptor agonist, and the effects of the desensitisation of P2X receptors with a,h-MeATP and of P2Y receptors with ADPhS were analysed recording the endoluminal pressure from whole-organ. ATP-induced relaxationwas antagonised by suramin, non-selective P2 receptor antagonist, by desensitisation of P2Y receptors with ADPhS, and increased bydesensitisation of P2X receptors with a,h-MeATP. a,h-MeATP produced biphasic responses: relaxation, reduced by P2X- or P2Ydesensitisation, and contraction, almost abolished by P2X desensitisation and potentiated by P2Y desensitisation. 2-MeSATP inducedrelaxation, which was antagonised by P2Y desensitisation and increased by P2X desensitisation. Tetrodotoxin increased the relaxationinduced by purines and deeply antagonised the contraction to a,h-MeATP. Our results suggest that in mouse stomach are present muscularP2Y receptors, subserving relaxation, and neuronal presynaptic P2X receptors, mediating contraction.