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We previously showed that bladder functions are controlled by clock genes with circadian rhythm. The sensation of bladder fullness (SBF) is sensed by mechano-sensor such as Piezo1 and TRPV4 in the mouse bladder urothelium. However, functional circadian rhythms of such mechano-sensors remain unknown. To investigate functional circadian changes of these mechano-sensors, we measured circadian changes in stretch-evoked intracellular Ca 2+ influx ([Ca 2+ ] i ) using mouse primary cultured urothelial cells (MPCUCs). Using Ca 2+ imaging, stretch-evoked [Ca 2+ ] i was quantified every 4 h in MPCUCs derived from wild-type (WT) and Clock Δ19/Δ19 mice, which showed a nocturia phenotype. Furthermore, a Piezo1 inhibitor GsMTx4 and a TRPV4 inhibitor Ruthenium Red were applied and stretch-evoked [Ca 2+ ] i in MPCUCs was measured to investigate their contribution to SBF. Stretch-evoked [Ca 2+ ] i showed a circadian rhythm in the WT mice. In contrast, Clock Δ19/Δ19 mice showed disrupted circadian rhythm. The administration of both GsMTx4 and Ruthenium Red eliminated the circadian rhythm of stretch-evoked [Ca 2+ ] i in WT mice. We conclude that SBF may have a circadian rhythm, which is created by functional circadian changes of Piezo1 and TRPV4 being controlled by clock genes to be active during wakefulness and inactive during sleep. Abnormalities of clock genes disrupt SBF, and induce nocturia.

The role of the P2Y 6 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 P2Y 6 receptor in lower urinary tract function of normal phenotypes by comparing P2Y 6 -deficient mice and wild-type mice. In in vivo experiments, P2Y 6 -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 P2Y 6 -deficient mice presenting markedly shorter bladder contraction duration but no difference in peak contraction pressure. However, analysis of in vitro experiments showed no P2Y 6 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 P2Y 6 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.