Regulation of Spontaneous Contractions in Intact Rat Bladder Strips and the Effects of Hydrogen Peroxide

Abstract

Enhanced spontaneous contractions are associated with overactive bladder. Elevated levels of reactive oxygen species might contribute to enhanced spontaneous contractions. We investigated the regulation of spontaneous contractions and the effects of hydrogen peroxide (H₂O₂) in intact rat bladder strips. The spontaneous contractions were measured using a tissue bath system. The vehicle or the specific activators/blockers were applied and followed by the application of 0.003 g% H₂O₂. The basal tension, amplitude, and frequency of spontaneous contractions were quantified. Nisoldipine and bisindolylmaleimide 1 had no effects on spontaneous contractions. SKF96365 and Y27632 decreased basal tension and amplitude. Ryanodine slightly increased frequency. Both iberiotoxin and NS-1619 increased amplitude. Apamin reduced frequency but increased amplitude. NS-309 inhibited both the amplitude and frequency. The basal tension and amplitude increased when H₂O₂ was applied. Pretreatment with NS-309 inhibited H₂O₂-elicited augmented amplitude and frequency, while pretreatment with Y-27632 inhibited the augmented basal tension. The combined application of NS-309 and Y27632 almost eliminated spontaneous contractions and its augmentation induced by H₂O₂. In conclusion, Ca²⁺ influx, Rho kinase activation, and SK channel inactivation play important roles in spontaneous contractions in intact bladder strips, whereas only latter two mechanisms may be involved in H₂O₂-elicited increased spontaneous contractions.

Figure 1

Representative tracings of spontaneous contractions of intact rat bladder strips before (Phase 1) and during (Phase 2) treatment with vehicle (0.1% DMSO) or test agent [nisoldipine (100 nM), SKF96365 (10 μM), ryanodine (10 μM), iberiotoxin (100 nM), NS1619 (30 μM), apamin (100 nM), NS309 (10 μM), Y27632 (10 μM), BIS-1 (2 μM), and Y27632 + NS309 (each 10 μM)] and then incubated with 0.003 g% H₂O₂ (Phase 3).

Figure 2

A zoomed image of spontaneous contraction tracings illustrating the quantified parameters. The spontaneous contractile events, the amplitude of which exceed 30% of the maximum response for the final 5 min in each 15 min incubation period, were used for analysis. For quantification of frequency, the contraction with multiple peaks due to partial relaxation (shown as a dashed arrow) was counted as one contraction event.