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).