P2Y6-deficiency increases micturition frequency and attenuates sustained contractility of the urinary bladder in mice

Satoru Kira,Schuichi Koizumi,Tsutomu Mochizuki,Mitsuharu Yoshiyama,Masayuki Takeda,Sachiko Tsuchiya,Tatsuya Miyamoto,Keisuke Shibata,Hiroshi Nakagomi,Eiji Shigetomi

doi:10.1038/s41598-017-00824-2

Satoru Kira, Schuichi Koizumi + Show 8 more

Open Access

https://doi.org/10.1038/s41598-017-00824-2

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Abstract

The role of the P2Y6 receptor in bladder function has recently attracted a great deal of attention in lower urinary tract research. We conducted this study to determine contributions of the P2Y6 receptor in lower urinary tract function of normal phenotypes by comparing P2Y6-deficient mice and wild-type mice. In in vivo experiments, P2Y6-deficient mice had more frequent micturition with smaller bladder capacity compared to wild-type mice; however, there was no difference between these groups in bladder-filling pressure/volume relationships during cystometry under decerebrate, unanaesthetized conditions. Analysis of in vivo bladder contraction revealed significant difference between the 2 groups, with P2Y6-deficient mice presenting markedly shorter bladder contraction duration but no difference in peak contraction pressure. However, analysis of in vitro experiments showed no P2Y6 involvements in contraction and relaxation of bladder muscle strips and in ATP release by mechanical stimulation of primary-cultured urothelial cells. These results suggest that the P2Y6 receptor in the central nervous system, dorsal root ganglion, or both is involved in inhibition of bladder afferent signalling or sensitivity in the pontine micturition centre and that the receptor in the detrusor may be implicated in facilitation to sustain bladder contraction force.

Highlights

P2Y receptors are G-protein-coupled receptors for extracellular nucleotides[1], which are classified into eight P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11–14)[2,3,4]
The expression of P2Y6 mRNA was widely distributed in the central nervous system (CNS), L6/S1 dorsal root ganglion (DRG), bladder and urethra (Fig. 1a)
No differences in the bladder pressure-volume relationship and the peak contraction pressures were found between the 2 groups, whereas the bladder contraction duration was prominently reduced in P2Y6-KO mice

Summary

Discussion

Compared with WT mice, P2Y6-KO mice showed markedly higher micturition frequency and smaller urination volume/voiding during voluntary voiding behaviour. Activation of urethral afferent pathway by urine leakage into the proximal urethra/bladder neck facilitates a voiding reflex[46], suggesting that a decrease in urethral tonus during bladder-filling would result in early release of the bladder fluid In agreement with this urethral mechanism, i.a. administration of sodium nitroprusside, a nitric oxide donor, which induces urethral relaxation with neither affecting bladder contractility nor stimulating bladder afferent transmission, produced prominent bladder overactivity in conscious rats[34]. The investigators showed that activation of the P2Y6 receptor enhances the P2X1-mediated contractile force and induces a sustained increase in in vitro bladder smooth muscle tone, further suggesting that the synergistic interaction between the P2X1 response and P2Y6 signalling is conducted through the phospholipase C (PLC)/inositol trisphosphate (IP3) pathway In agreement with their result[18], the present cystometry experiments showed that bladders of P2Y6-KO mice are unable to sustain the contraction force for as long a duration as those of WT mice. It is of interest to investigate, in other species including humans, whether malfunction or blockade of the P2Y6 receptor generates lower urinary tract symptom such as bladder overactivity

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