3.4 Release of SP and PGE2 contribute to H2O2-induced enhancement effects
Tachykinins are neuropeptides present in the capsaicin-sensitive primary afferents of the urinary bladder of various species (including humans). Release of these peptides in the periphery produced prominent effects on the SBCs of isolated bladder strips[3]. In agreement with this report, application of SP (500nM) increased the SBCs of human-bladder strips significantly (Fig. 5A), and the enhancing effect of SP could be blocked by a specific antagonist of NK2Rs: SR 48968 (10μM). AUC and Δg were reduced by 84.5% and 64.3%, respectively (Fig. 5A, B). NK2R is the main subtype of neurokinin receptor that mediates the effects of neurokinins in the human bladder[40-42]. SR 48968 applied alone did not impact the contractile activity. As expected, the NK2R antagonist SR 48968 (10μM) reduced the H2O2(100μM)-induced increase in SBCs significantly (Fig. 5C). AUC and Δg were reduced by 74.1% and 49.1%, respectively (Fig. 5D), which suggested that SP release contributed to the enhancement effects of H2O2.
PGE2 released from sensory afferents, urothelial cells, or the detrusor has been shown have important modulatory effects on SBCs in vitro [43] and voiding behavior in vivo [44]. In agreement with those reports, application of PGE2 (1μM) evoked a significant increase in the SBCs of human-bladder strips (Fig. 6A). Pretreatment (15 min before H2O2) with indomethacin (10μM) to block the synthesis and release of PGE2 led to significant attenuation of H2O2 (100μM)-induced effects, with AUC and Δg being reduced by 65.9% and 35.9%, respectively (Fig. 6B and C). Indomethacin (10μM) applied alone did not affect contractile activity. This observation indicated that PGE2 release contributed to the enhancing effects of H2O2.