Login to Access Video or Poster Abstract: MP42-20
Sources of Funding: NHMRC Australia

Introduction

Studies suggest that the symptoms associated with overactive bladder syndrome (OAB) and interstitial cystitis (IC) may be due to a disrupted mucosal barrier. Access of the urine to underlying sensory structures is hypothesised to induce bladder irritation which, in the absence of an ability to ‘scratch’ is manifest in the symptoms of urinary urgency and frequency. The TGR5 and MRGPR receptors have been implicated in mediating non-histaminergic itch responses in the skin and are responsible for bile acid, protease, and chloroquine induced pruritis (itch). Bile acids are secreted in high concentrations in the urine and we hypothesise that these itch mediators may be a novel mechanism responsible for the sensory abnormalities seen in OAB and IC.

Methods

Ex-vivo bladder afferent recordings were used to identify the role of TGR5 in bladder mechanosensation. Retrogradely traced bladder DRG neurons from C57/BL6 mice were isolated, dissociated and used for single cell RT-PCR. The TGR5 receptor agonist CCDC (10μM), and the MRGPR C11 and A3 agonists chloroquine (1μM), NPFF (2μM), and BAM 8-22 (2μM) were used in calcium imaging and whole cell patch clamp recordings from bladder DRG neurons.

Results

Single cell PCR data identified TGR5, MRGPR-C11, and MRGPR-A3 receptor mRNA expression in bladder afferent neurons. CCDC, chloroquine, NPFF, and BAM 8-22 were able to induce large calcium transients in 60% of bladder neurons. Application of CCDC/MRGPR mixed agonists to bladder DRG neurons induced significant hyperexcitability, with a significant reduction in rheobase (p≤0.001), and a significant increase in the frequency of action potentials at 2X rheobase (p≤0.01) compared to control. Intravesical infusion of CCDC into the bladder induced significant mechanical hypersensitivity to bladder distension (p≤0.001) with no change in muscle compliance.

Conclusions

This data shows for the first time that TGR5 and MRGPR receptors are functionally present on bladder DRG neurons and their activation is able to induce calcium transients, neuronal hyperexcitability and mechanical hypersensitivity. This suggests that histamine-independent itch mechanisms are not exclusive to somatic pathways, but are present and functional in the viscera and may be important in bladder hypersensitivity pathologies.

Funding

NHMRC Australia