a. Mean pH responses of S-b sensilla in genotypes as indicated. Genotypes were: w1118 (wild-type) n=12, Ir64aMB05283 (Ir64a) n=5, Gr33a1 (Gr33a) n=6, painEP2621 (painless) n=6, TrpA11 (TrpA1) n=6, and Pkd21 (Pkd2) n=7. **P < 0.01 versus wild-type, 2-way ANOVA with Tukey’s post hoc analysis. For each genotype, at least two independent flies were tested on the same day. Error bars = s.e.m. b,c. Representative traces and mean responses of wild-type S-b labellar sensilla to standardized HCl solutions at indicated pH alone n=12 (0 or −) or in mixtures with ZnCl2 (n=10 for 1mM ZnCl2 and n=4 for 10mM ZnCl2) or amiloride hydrochloride n=5–7. Neither ZnCl2 (Student’s t-test) nor amiloride hydrochloride (2-way ANOVA with pairwise comparisons) caused any change in pH response. Vertical bar = 1 mV; horizontal bar = 100 ms. Error bars = s.e.m.