NKA enhances bladder-afferent mechanosensitivity via urothelial and detrusor activation

Abstract

Tachykinins are expressed within bladder-innervating sensory afferents and have been shown to generate detrusor contraction and trigger micturition. The release of tachykinins from these sensory afferents may also activate tachykinin receptors on the urothelium or sensory afferents directly. Here, we investigated the direct and indirect influence of tachykinins on mechanosensation by recording sensory signaling from the bladder during distension, urothelial transmitter release ex vivo, and direct responses to neurokinin A (NKA) on isolated mouse urothelial cells and bladder-innervating DRG neurons. Bath application of NKA induced concentration-dependent increases in bladder-afferent firing and intravesical pressure that were attenuated by nifedipine and by the NK2 receptor antagonist GR159897 (100 nM). Intravesical NKA significantly decreased bladder compliance but had no direct effect on mechanosensitivity to bladder distension (30 µl/min). GR159897 alone enhanced bladder compliance but had no effect on mechanosensation. Intravesical NKA enhanced both the amplitude and frequency of bladder micromotions during distension, which induced significant transient increases in afferent firing, and were abolished by GR159897. NKA increased intracellular calcium levels in primary urothelial cells but not bladder-innervating DRG neurons. Urothelial ATP release during bladder distention was unchanged in the presence of NKA, whereas acetylcholine levels were reduced. NKA-mediated activation of urothelial cells and enhancement of bladder micromotions are novel mechanisms for NK2 receptor-mediated modulation of bladder mechanosensation. These results suggest that NKA influences bladder afferent activity indirectly via changes in detrusor contraction and urothelial mediator release. Direct actions on sensory nerves are unlikely to contribute to the effects of NKA.

An ex vivo bladder model with detrusor smooth muscle removed to analyse biologically active mediators released from the suburothelium

“…; Grundy et al . ). Such assumptions, however, overlook possible differential regulation of release and/or metabolism of mediators at the apical and basolateral sides of urothelium that other studies have suggested (Yu et al .…”

“…Such concerns apply to both the use of the entire bladder wall and of isolated bladder mucosa as flat sheets. Some studies have measured release of mediators into the bladder lumen during filling and assumed that luminal release of mediators reflects the profile of mediators in subU/LP where afferent nerves and other cells with receptors for urothelial mediators might reside (Daly et al 2014;Beckel et al 2015;Gonzalez et al 2016;Grundy et al 2018). Such assumptions, however, overlook possible differential regulation of release and/or metabolism of mediators at the apical and basolateral sides of urothelium that other studies have suggested (Yu et al 2006;Yu, 2015).…”

Experimentally Induced Bladder Permeability Evokes Bladder Afferent Hypersensitivity in the Absence of Inflammation

“…Whilst we did not investigate the precise mechanism driving bladder afferent sensitivity in this study, it is likely that as urothelial permeability is increased, urinary contents gain access to afferent nerves to either cause afferent hypersensitivity directly, or indirectly via actions on urothelial cells. We and others have shown that a variety of endogenous mediators can activate bladder afferents, causing afferent hypersensitivity (de Groat and Yoshimura, 2009;Birder and Andersson, 2013;Yoshimura et al, 2014;Grundy et al, 2018b;Konthapakdee et al, 2019;Grundy et al, 2020).…”

Serotonin exerts a direct modulatory role on bladder afferent firing in mice

“…Bladder afferent nerve activity was determined using an ex vivo model previously described (Daly et al 2007;Grundy et al 2018a). The whole bladder and surrounding tissues (together with its emanating nerve fibres) was placed in a recording chamber (30 ml).…”

“…Information regarding the state of bladder distension is carried via sensory afferents that project via the pelvic and hypogastric nerves into the dorsal horn of the spinal cord, feeding into autonomic reflex and micturition centres within the brainstem to maintain continence (see Grundy et al 2018a for review). Bladder afferents are found innervating both the detrusor smooth muscle and the urothelium (Spencer et al 2018), consisting of myelinated Aδ fibres and unmyelinated C fibres that exhibit polymodal sensitivity to a host of mechanical and chemical stimuli (Su & Gebhart, 1998;Zagorodnyuk et al 2006Zagorodnyuk et al , 2007.…”