Fig. 1. (A) Mean force developed in gastric smooth muscle under basal conditions in prometamorphic (Promet.), metamorphic (Met.) and juvenile Xenopus. Statistical significance was calculated using a one-way ANOVA followed by Bonferroni's post hoc test (N=28). (B) Concentration-dependent increase in mean force in response to carbachol (CCh). Statistically significant increase was obtained at 1 µmol l^–1 at all stages (N=6). (C) Concentration-dependent increase in mean force in response to neurokinin A (NKA). A statistically significant increase was obtained at 0.1 µmol l^–1 for prometamorphosis (N=7) and metamorphosis (N=8), and at 1 µmol l^–1 for juveniles (N=6). For concentration–response curves, statistical analysis was performed using repeated measures one-way ANOVA followed by Dunnett's post hoc test. Control value prior to administration of agonist is denoted C on the x-axis. (D) Effect of 300 µmol l^–1 N-nitro-L-arginine methyl ester hydrochloride (L-NAME) administered 20–30 min prior to measurements in prometamorphosis (N=7), metamorphosis (N=8) and juveniles (N=9). Asterisk indicates a statistically significant difference, P<0.05. (E,F) Representative traces of the response to L-NAME (300 µmol l^–1) in (E) metamorphic tissues and (F) juvenile tissues.