Abstract Background and purpose: Several studies have indicated that reactive oxygen species (ROS) can lead to detrusor overactivity (DO), but the underlying mechanisms are not known. Hydrogen dioxide (H2O2) is used commonly to investigate the effects of ROS. In present study, we aimed to investigate the effects of H2O2 on phasic spontaneous bladder contractions (SBCs) of isolated human-bladder strips (iHBSs) and the underlying mechanisms. Experimental approach: Samples of bladder tissue were obtained from 26 patients undergoing cystectomy owing to bladder cancer. SBCs of iHBSs were recorded in organ-bath experiments. Immunofluorescence staining was conducted to confirm the TRPA1 expression on sensory nerves. Key results: H2O2 (1μM–10mM) concentration-dependently increased the SBCs of iHBSs. These enhancing effects could be mimicked by an agonist of transient receptor potential (TRP)A1 channels (allyl isothiocyanate) and blocked with an antagonist of TRPA1 channels (HC030031; 10μM). H2O2 induced enhancing effects also could be attenuated by desensitizing sensory afferents with capsaicin (10μM), blocking nerve firing with TTX (1μM), blocking neurokinin effects with NK2 receptor antagonist (SR48968, 10μM), and blocking PGE2 synthesis with indomethacin (10μM), respectively. Conclusions and implications: Our study: (i) suggests activation of TRPA1 channels on bladder sensory afferents, and then release of substance P or PGE2 from sensory nerve terminals, contribute to the H2O2-induced enhancing effects on SCs of iHBSs; (ii) provides insights for the mechanisms underlying ROS leading to DO; (iii) indicates that targeting TRPA1 channels might be the promising strategy against overactive bladder in conditions associated with excessive production of ROS.

Abstract Background and purpose: 5-Hydroxytryptamine (5-HT) can enhance human ureteral contractions. However, the mediating receptors have not been clarified yet. The study sought to further characterize the mediating receptors using several more selective antagonists and agonists. Experimental approach: Human distal ureters were obtained from 88 patients undergoing cystectomy. The mRNA expression levels of 5-HT receptors were examined using RT-qPCR experiments. The phasic contractions of ureter strips, either spontaneous or evoked with neurokinin, were recorded in an organ bath. Key results: Among the 13 5-HT receptors, 5-HT2A and 5-HT2C had the highest mRNA expression levels. 5-HT (10-7–10-4 M) concentration-dependently increased the frequency and baseline tension of phasic contractions. However, a tachyphylaxis effect was observed. SB242084 (100 nM) and ketanserin (100 nM), which are 5-HT2C selective and non-selective antagonist, respectively, shifted the 5-HT concentration-response curves (frequency and baseline tension) rightward. 5-HT2C selective agonist, vabicaserin, increased contraction frequency with an Emax of 35% of 5-HT. 5-HT2A selective antagonist, volinanserin (100 nM), only reduced baseline tension. The selective antagonists of 5-HT1A,1B, 1D, 2B, 3, 4, 5, 6, and 7 had no antagonism. Blockade of voltage-gated sodium channels, α1-adrenergic receptors, adrenergic neurotransmission, and neurokinin-2 receptors using tetrodotoxin, tamsulosin, guanethidine, and Men10376, respectively, and desensitizing sensory afferents using capsaicin (100 μM), significantly reduced 5-HT effects. Conclusion and implications: 5-HT enhanced ureteral phasic contractions mainly by activating 5-HT2C. Activation of sympathetic nerve and sensory afferents partly contributed to 5-HT effects. 5-HT and 5-HT2C receptors could be promising targets for ureteral stone expulsion and ureteral colic relief.