Cumulative concentration–response curves to purine agonists on AVP (10 nM) precontracted urethral strips. (a) Concentration–response curves to ATP (0.1 μM–1 mM) in the absence and presence of MRS2170 (1–30 μM). (b) Concentration–responses curves to α,β-meATP, β,γ-meATP and 2-MeSATP (all 0.1 μM–1 mM) in the absence and presence of MRS2179 (10 μM). All points show the mean±s.e.m. of six to eight experiments, unless occluded by the symbol. **P<0.01, ***P<0.001, following a two-way ANOVA and Tukey's post hoc test.