3.1 H2O2 enhanced the spontaneous phasic contractions of isolated human-bladder strips in a concentration-dependent manner
We found that 112 of 186 (60%) of human-bladder strips displayed phasic SBCs during an equilibration period of 30–40 min. Nevertheless, SBCs were evoked with carbachol (1nM). Carbachol (1nM) treatment increased the baseline tension by 1.2 ± 0.3 g (n = 62 strips).
Application of H2O2(from 1μM to 10mM) produced a concentration-dependent increase in the SBCs of human-bladder strips (Fig. 1A). This enhancement manifested mainly as an increase in the baseline tone and amplitude of phasic contractions, and there was no change in the frequency of phasic contractions (Fig.1A). The enhancement could last >20 min. Therefore, the response to H2O2 was evaluated with the percent increase in AUC as well as the net change of Δg from the control. A significant desensitization effect was observed at higher doses (≥100μM) of H2O2(Supplementary Fig. 1). Thus, noncumulative concentration–response curves of H2O2 were established (Fig. 1C) and revealed an EC50 of 175.8μM and 40.3μM for AUC and Δg, respectively (Fig. 1C). We did not see the inhibitory effects of H2O2 during a 30-min observation period for any concentration. There was no significant difference in the amplitude of the H2O2 (100μM)-induced increase in Δg between carbachol-treated (Δg = 0.85 ± 0.12g/g, n = 12) and untreated strips (Δg = 0.78 ± 0.23g/g, n = 7).