The Use of the Isolated Mouse Whole Bladder for Investigating Bladder Overactivity

Abstract

The isolated mouse whole bladder was used to study in vitro bladder overactivity evoked by intramural nerve sensitization with bradykinin, mimicking neurogenic bladder overactivity secondary to bladder inflammation. Intravesical pressure responses to intramural electrical stimulation of intramural nerves were measured under isovolumetric condition. Validation showed that carbachol produced a dose-response curve closely mirroring that observed in the isolated muscle strips and demonstrated the dual nature of electrically evoked neurotransmission, consisting of a cholinergic component largely mediated by M₃ receptors and a purinergic component mediated by P2X receptors. ATP generated a biphasic dose-response curve, suggesting that the P2X receptors may be heterogeneous in distribution. Characterization of bradykinin receptors showed bradykinin to be extremely potent in exciting the bladder, producing a dose-response curve with an EC₅₀ of 90 nM, and bradykinin also enhanced electrically evoked bladder contractions. These effects were inhibited by the B₂ receptor antagonist HOE 140 (d-Arg⁰-Arg¹-Pro²-Hyp³-Gly⁴-Thi⁵-Ser⁶-d-Tic⁷-Oic⁸-Arg⁹) but not the B₁ receptor antagonist desArg¹⁰ HOE 140 (H-d-Arf-Arg-Pro-Hyp-Gly-Thi-Ser-d-Tic-Oic-OH) and were also modulated by α,β,methyleneATP. The isolated mouse whole bladder has proved a viable, robust model in which to demonstrate the pharmacological characteristic of the bladder and adds to the repertoire of in vitro tools for investigating potential therapeutic agents.