Length dependence of resting and KCl-induced force in WT, KO, and HET intact urinary bladder strips. (A) Original force tracings of 80 mM KCl elicited force at 1.1L₀. In the majority of WT strips, KCl elicited a biphasic contraction; P1, peak 1; P2, peak 2. (B–D) Summary of results. The plateau force was determined 5 min after addition of KCl. Symbols represent mean ± SEM from 10 WT, 13 KO, and 9 HET bladder strips (1 per fetus) taken from 8 litters. *, P < 0.05 (two-way ANOVA, Sidak’s multiple comparisons test).