Contractile parameters in intact E18.5 urinary bladder aorta. At the end of the protocol shown in Fig. 10, the bladder strips were stimulated with increasing concentrations of carbachol (CCh) at L = 1.5L₀. (A) Original force tracings of a WT and a KO urinary bladder strip; force responses in HET were similar (not depicted). (B and C) Summary of results. Peak denotes the initial maximal tonic response, and plateau, the tonic response after 5-min stimulation. Bars represent mean ± SD (symbols represent determinations from individual fetuses; cf. Fig. 10). Force in KO elicited by 3 µM CCh tended to be lower in KO, and in HET at 10 and 30 µM CCh higher than in WT, without reaching the level of significance. (D) Original force tracings from ring preparations of the abdominal aorta, which shows the force response to stepwise stretching (dots) and release to IC₉₀ (upward arrow) according to the Mulvany normalization protocol (see Materials and methods). RF, resting force before addition of U46619, and the response to increasing concentrations of U46619. (E) Relation between force and stretch during normalization protocol (n = 3 WT and n = 3 KO fetuses). (F) U46619 concentration–response curve. Symbols represent mean ± SEM, and lines represent the sigmoidal fits, which are significantly different between groups. (G) Summary of resting force (RF) before application of U46619, and F_max = total force. Symbols represent force responses from five WT and seven KO fetuses from five litters (one preparation per animal). Bars: mean ± SD; n.s., not significant (P = 0.07); ***, P < 0.001 (two-way ANOVA, uncorrected Fisher’s least significant difference posttest).