Prostaglandin E2 excitatory effects on guinea pig urinary bladder smooth muscle: a novel regulatory mechanism mediated by large-conductance voltage- and Ca2+-activated K+ channels.

Prostaglandin E2 (PGE2) is an essential signaling molecule involved in the regulation of detrusor smooth muscle (DSM) function. However, the underlying regulatory mechanism by which PGE2 augments DSM cell excitability and contractility is not well understood. Here, we investigated whether PGE inhibits the large conductance voltage- and Ca2+-activated K+ (BK) channels in guinea pig DSM, thereby increasing DSM excitability and contractility. We used a multidisciplinary experimental approach including amphotericin–B perforated patch-clamp electrophysiology and live-cell Ca2+ imaging in native freshly-isolated DSM cells, isometric tension recordings of intact DSM strips, and pharmacological tools to investigate BK channel regulation by PGE2 in guinea pig DSM. PGE2 increased the spontaneous phasic contractions of isolated DSM strips in a concentration-dependent manner (10 nM-10 μM). BK channel inhibition with paxilline (1 μM) attenuated the PGE2-induced DSM phasic contractions, suggesting that BK channels are involved in the mechanism of PGE2-induced DSM contractions. PGE2 (10 μM) increased the intracellular Ca2+ levels in freshly-isolated DSM cells. PGE2 (10 μM) also caused an inhibition of the amplitude and frequency of spontaneous transient BK currents in DSM cells. Moreover, PGE2 (10 μM) did not affect the amplitude of whole cell steady-state BK currents in DSM cells. Our findings provide strong experimental evidence that PGE2 leads to an inhibition of the spontaneous transient BK currents, elevation of intracellular Ca2+ levels in freshly-isolated DSM cells, and augmentation of DSM phasic contractions. Thus, we have revealed a novel mechanism that BK channels mediate PGE2-induced contractions in guinea pig DSM.

前列腺素E2（PGE2）是一种参与调节逼尿肌平滑肌（DSM）功能的重要信号分子。然而，PGE2增强DSM细胞兴奋性和收缩性的潜在调节机制尚不清楚。在此，我们研究了PGE2是否抑制豚鼠DSM中的大电导电压和钙离子激活的钾离子（BK）通道，从而增加DSM的兴奋性和收缩性。我们采用了多学科的实验方法，包括两性霉素B穿孔膜片钳电生理学和在新鲜分离的原代DSM细胞中的活细胞钙离子成像、完整DSM条带的等长张力记录以及药理学工具，以研究PGE2对豚鼠DSM中BK通道的调节。PGE2以浓度依赖的方式（10 nM - 10 μM）增加了分离的DSM条带的自发性阶段性收缩。用帕西林（1 μM）抑制BK通道可减弱PGE2诱导的DSM阶段性收缩，这表明BK通道参与了PGE2诱导的DSM收缩机制。PGE2（10 μM）增加了新鲜分离的DSM细胞内的钙离子水平。PGE2（10 μM）还导致DSM细胞中自发性瞬时BK电流的幅度和频率受到抑制。此外，PGE2（10 μM）不影响DSM细胞中全细胞稳态BK电流的幅度。我们的研究结果提供了强有力的实验证据，表明PGE2导致新鲜分离的DSM细胞中自发性瞬时BK电流受到抑制、细胞内钙离子水平升高以及DSM阶段性收缩增强。因此，我们揭示了一种新的机制，即BK通道介导豚鼠DSM中PGE2诱导的收缩。