In vivo paracrine effects of ATP-induced urothelial acetylcholine in the rat urinary bladder.

Johanna Stenqvist,Thomas Carlsson,Gunnar Tobin,Patrik Aronsson,Michael Winder

doi:10.1016/j.autneu.2020.102689

Johanna Stenqvist, Thomas Carlsson + Show 3 more

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https://doi.org/10.1016/j.autneu.2020.102689

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Abstract

Mechanical stretch of the urothelium induces the release of ATP that activates bladder afferent nerves. In the rat urinary bladder, ATP is also a contractile co-transmitter in the parasympathetic innervation. In isolated preparations, ATP evokes a urothelial release of acetylcholine that substantially contributes to ATP-evoked contractile responses. Currently we aimed to further examine the interactions of ATP and acetylcholine in the rat urinary bladder in two in vivo models. In the whole bladder preparation, atropine reduced ATP-evoked responses by about 50% in intact but denervated bladders, while atropine had no effect after denudation of the urothelium. In a split bladder preparation, reflex-evoked responses of the contralateral half were studied by applying stimuli (agonists or stretch) to the ipsilateral half. Topical administration of ATP and methacholine as well as of stretch induced contralateral reflex-evoked contractions. While topical administration of atropine ipsilaterally reduced the ATP- and stretch-induced contralateral contractions by 27 and 39%, respectively, the P2X purinoceptor antagonist PPADS reduced them by 74 and 84%. In contrary, the muscarinic M2-(M4)-selective receptor antagonist methoctramine increased the responses by 38% (ATP) and 75% (stretch). Pirenzepine (M1-selective antagonist) had no effect on the reflex. In vitro, in the absence of the reflex, methoctramine did not affect the ATP-induced responses. It is concluded that urothelial ATP potently induces the micturition reflex and stimulates urothelial release of acetylcholine. Acetylcholine subsequently acts on afferents and on the detrusor muscle. While muscarinic M2 and/or M4 receptors in the sensory innervation exert inhibitory modulation, muscarinic M3 receptors cause excitation.

Highlights

The urothelium has important signaling and sensory functions and plays a crucial role for the initiation of the micturition reflex
We have shown in in vitro studies that adenosine 5′-triphosphate disodium salt hydrate (ATP) evokes a release of acetylcholine from the urothelium and that this release substantially contributes to the ATP-evoked detrusor contractile response (Stenqvist et al, 2017; Stenqvist et al, 2018)
The current study confirms that ATP exerts effects on the afferent and efferent levels of the micturition reflex arc in the rat urinary bladder

Summary

Introduction

The urothelium has important signaling and sensory functions and plays a crucial role for the initiation of the micturition reflex. ATP released from the urothelium induced by mechanical stretch has been considered to be an important signaling substance for activating bladder afferent nerves (Ford et al, 2006). Purinoceptors of the P2X2, P2X3 and/or P2X2/3 have been described on the afferent nerves (Cockayne et al, 2000; Cockayne et al, 2005) as the targets for ATP when inducing bladder sensation. The significance of the P2X3 purinoceptor is elucidated by the findings in knockout mice, which exhibit urinary bladder hyporeflexia (Cockayne et al, 2005). The exact roles of the different urothelium-derived substances are far from unraveled, but indicate the importance of the urothelium for bladder function. The complexity of the possible roles of the urothelium is underlined by the fact that all five muscarinic and all seven P2X purinergic receptors, as well as some P2Y purinergic and nicotinic receptor subtypes are expressed in the tissue (Bschleipfer et al, 2007; Birder et al, 2004; Beckel and Birder, 2012)

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