The mechanosensitive Ca2+ permeable cation channel TRPV4 is expressed in the urothelium and detrusor smooth muscle (DSM) of rodent bladders (Thorneloe et al., 2008). Urothelial stretch during bladder filling activates TRPV4 and produces a Ca2+-dependent release of ATP (Mochizuki et al., 2009). We have recently identified enhanced muscarinic contractions and impaired adrenergic relaxation in bladder strips from male TRPV4 knockout mice, suggesting the release of an inhibitory factor from the urothelium. We hypothesised that deletion of TRPV4 would similarly enhance muscarinic contractions in bladder strips from female mice. Male and female C57BL/6 wild type (+/+) and TRPV4 knockout (-/-) mice (22-30g) were used in this study. Bladders were lysed in RIPA buffer and separated by PAGE. TRPV4 / GAPDH expression was quantified by Western blotting / densitometry. For functional experiments, bladders were collected, sectioned above the level of the ureters, then cut into 2 longitudinal strips. These were suspended under 0.5g tension in a 10ml organ bath containing Krebs’ solution (pH7.4) at 37oC and bubbled with 95% O2 and 5% CO2. Changes in isometric force were recorded using a Power Lab v.4 system (AD Instruments, UK). Concentration-response curves to carbachol and KCl were constructed. Following pre-contraction of the tissue strips with 80mM KCl, a concentration-response curve was obtained for relaxation to the β-adrenergic agonist isoprenaline. Frequency-response curves to electrical field stimulation (EFS: 10s; 80V; pulse width 1ms) were also obtained. Emax values (stated as mean±S.E.M) were compared by unpaired t-tests. Maximal contractions to carbachol were significantly increased in TRPV4 -/- strips from male mice (1nM-30μM; +/+ = 0.040±0.003 vs -/- = 0.091±0.005g/mg, p<0.05, n=9). Maximal carbachol contractions were greater in strips from female mice than male mice, but without any genotype difference (+/+ = 0.106±0.007 vs -/- = 0.120±0.006g/mg, n=8). Similarly, contractions to EFS (2,4,8,16,32Hz) were greater in bladder strips from female mice than male mice, and there was no genotype difference. Maximal relaxation to isoprenaline (1nM-30µM; +/+ = 49.3±2.4 vs -/- = 53.0±2.1 % of KCl contraction, n=6) and maximum contraction to KCl (1mM-300mM; +/+ = 0.092±0.015 vs -/- = 0.108±0.008g/mg, n=5) were unaffected by TRPV4 deletion in female bladder strips. Expression of TRPV4 was lower in female bladders than male bladders (TRPV4/GAPDH ratios: Male = 0.40±0.06 vs female: 0.22±0.05, n=5). These data suggest that decreased TRPV4 expression and / or impaired function contributes to enhanced muscarinic contractions in wild type female bladder strips, and may underlie sex differences in bladder physiology in other species.