Involvement of stretch-induced Rho-kinase activation in the generation of bladder tone†‡

Aims The present study investigated the role of the Rho-kinase (ROK) pathway in the maintenance of bladder tone during the storage phase, and its effects on bladder compliance. Methods Muscle strips from isolated rat bladder (detrusor strips) were used to evaluate the effects of the ROK inhibitors Y-27632 and HA-1077 on resting tension, which is independent of G-protein coupled pathways. Stretch-induced ROK activation was assessed by measuring phosphorylation of MYPT1 (myosin phosphatase targeting subunit) using Western blotting. The effect of ROK inhibitors on bladder compliance during bladder filling was assessed in an in vitro whole bladder model. Results Y-27632 and HA-1077 caused concentration-dependent relaxation of detrusor strips. Stretch increased MYPT1-p[Thr853] levels by approximately 1.5-fold in normal Krebs buffer. The ROK inhibitor Y-27632 abolished the stretch-induced increase and reduced the level of MYPT1-p[Thr853] to <50% of the basal values in normal Krebs buffer. Stretch-induced phosphorylation of MYPT1 was independent of Ca2+ originating from either extracellular or intracellular stores. When tested in the isolated whole rat bladder model, HA-1077 significantly increased bladder compliance at both 3 and 10 µM. Conclusions This study demonstrates that the ROK pathway is constitutively active and stretch further activates the ROK pathway, which contributes to the generation of bladder tone, thereby affecting bladder compliance. Neurourol. Urodynam. 32: 1019–1025, 2013. © 2012 Wiley Periodicals, Inc.