P2X₃Expression Levels And Electrophysiological Characteristics In Interstitial Cells Of Cajal In Rats With Partial Bladder Outlet Obstruction

PBOO results in changes in bladder structure and function, which can lead toan overactive bladder （OAB）. Recently, the role of ICCs in the pathophysiologyof OAB has become the focus of intensive interesting. These specialmesenchymal cells, named myofibroblasts, ICCs, or interstitial cells （ICs） werefirst recognized in the gut. ICCs act as primary pacemaker cells which initiatespontaneous slow waves and corresponding phasic contractions, and play afundamental role in the transmission of signals from enteric neurons to smoothmuscle cells. In the urinary bladder, histological studies demonstrate that anetwork of functionally connected ICCs are located between the sensory nerveendings and urothelium, and might transfer signals directly between them..Studies have shown that the numbers of ICCs in OAB patients are significantlyhigher than normal. Inhibition of ICCs activity can reduce the spontaneousactivity of the detrusor muscle in OAB patients. Moreover, ultrastructural features of ICCs changed in the PBOO model.Adenosine triphosphate （ATP） is identified as a motor neurotransmitter inthe urinary bladder of the guinea pig in1972. The mechanotransduction betweenbladder filling and afferent activation have been studied, indicating thatstretching of the urothelium releases ATP. P2X₃is most closely involved in theprimary sensory effects of ATP, as it plays an important role in the painsignaling machinery. P2X₃receptors knockout mice exhibit bladderhyporeflexia on cystometry with decreased voiding frequencies, increasedbladder capacities, but normal bladder pressures.Numerous studies have shown that P2X₃receptors play important roles inmechanosensory transduction. But few methods have been available toinvestigate the relative contribution of these receptors to specific sensorybehaviours in ICCs. Thus, P2X₃receptors may play a crucial role in themicturition reflex pathway. Our previous study demonstrated that a network ofsuburothelial ICCs had close associations with afferent nerve fibers, and theP2X₃receptors staining was extensively distributed in the bladder suburothelialICCs. The ICCs that are present in cases of bladder overactivity seem to produceabnormal sensory signals mediated by the P2X₃receptors. However, detailedmechanisms underlying remained to be understood. In the present study, weinvestigated the changes in expression and function of P2X₃receptors in thebladder ICCs of rats with PBOO. In addition, the relationship between PBOOand changes in P2X₃receptors was determined.ObjectiveTo investigate the expression and electrophysiological characteristics ofP2X₃receptors in ICCs at different time points in a rat model of PBOO. Method（s）1. The studies were performed on48female Sprague-Dawley rats. The rats weredivided randomly into four groups:4,6and8wk PBOO groups andsham-operated controls. Four weeks after surgery, cystometry was performed todetect bladder function in vivo. Subsequently, subjects were killed at wk4,6or8and the bladders were harvested for measurements.2. P2X₃expression in ICCs of bladder was examined by immunofluorescenceanalyses.3. The level of P2X₃mRNA was explored by RT-PCR.4. Inward currents in corresponding ICCs in rat a model of PBOO wereobserved by electrophysiological technique.Result（s）1. Cystometrography showed a significant increase in the maximum detrusorpressure in rats subjected to PBOO. There were no significant differences inbladder compliance among the experimental groups.2. There was a significant increase in the intensity of P2X₃staining in ICCs inall PBOO groups than that in the control group which showed a time-dependentmanner.3. RT-PCR revealed that the expression of P2X₃mRNA was remarkableup-regulated at4,6and8wk in ICCs from the PBOO animals.4. The mean peak amplitude of inward currents was significantly increased inICCs in the PBOO than in the control group.ConclusionThese studies demonstrate that P2X₃receptors up-regulation in a time-dependent manner in ICCs from an experimental rat model of PBOO. P2X₃receptor agonist, α, β-meATP, enhanced the inward currents in PBOO ICCs.Furthermore, The results indicated that the up-regulation of P2X₃in bladderICCs may contribute to the pathophysiology of bladder overactivity.