Proceedings of The Physiological Society

University College Dublin (2009) Proc Physiol Soc 15, PC183

Poster Communications

Altered urothelial ATP signaling in human Overactive Bladder (OAB) patients

W. Tan2, A. Contreras-Sanz1, T. Kennedy-Lydon1, S. L. Alexander1, S. Janska1, S. Bishara2, R. Lunawat2, R. Khasriya2, K. M. Taylor3, C. Crawford1, J. Malone-Lee2, S. S. Wildman1

1. Urinary System Physiology Unit, Royal Veterinary College, London, United Kingdom. 2. Department of Medicine, University College London, Whittington Campus, London, United Kingdom. 3. Department of Pharmaceutics, The School of Pharmacy, University of London, London, United Kingdom.

Overactive bladder (OAB) is characterized by frequency, urgency and urge-incontinence, in the absence of urinary infection. We have identified a previously unrecognized pyuria (≥10 white blood cell/µl urine) in a majority of patients diagnosed as having OAB; associated with more severe symptoms(1). It is established that extracellular ATP signalling, originating from stretch-evoked ATP release and necessarily involving activation of a variety of P2 receptors, is involved in bladder sensation(2). Furthermore, inflammation is associated with increased ATP release from epithelial cells(3). Taken together, we hypothesise that in pyuric OAB patients, there is increased ATP release and/or increased P2 receptor expression, caused by inflammation, which ultimately results in increased sensory nerve excitation and the exacerbation of OAB symptoms. Here we begin to investigate our hypothesis. Bladder urothelium biopsies were obtained from i) asymptomatic patients, ii) pyuric OAB patients, and iii) non-pyuric OAB patients, using flexible cystoscopy. Basal and hypotonicity-evoked (i.e. stretch-evoked) ATP release from urothelium was quantified using a luciferin/luciferase assay, P2 receptor mRNA levels were investigated using quantitative real time-PCR, and P2 receptor expression was investigated in snap-frozen sliced tissue using immunohistochemistry. Basal ATP release was 50-fold greater from the urothelium of pyuric OAB patients (P<0.01; n=10) than from non-pyuric OAB (n=9) or asymptomatic patients (n=9). In contrast, in all three patient groups, the concentration of ATP released following stretch was similar. Basal and stretch-evoked ATP release was significantly abolished (P<0.01; n=3) by addition of the P2 receptor antagonist suramin (1 mM). In asymptomatic patient urothelium, we detected significant levels of P2X1-3,5-7 subunit and P2Y1,2,6,11-14 receptor mRNA (n=6). Urothelium from pyuric OAB patients showed a significant increase in abundance of P2X5 subunit and P2Y2,11,12 receptor mRNA, and a significant decrease in abundance of P2X1 subunit mRNA (P<0.01; n=3). Urothelium from non-pyuric OAB patients showed a significant increase in P2Y11 mRNA (P<0.01, n=3). Immunohistochemisty confirmed our real time-PCR data (n=3). In summary, this data demonstrates that in a subset of OAB patients (those with pyuria) there is increased basal ATP release from the urothelium, which is abolished by the P2 receptor antagonist suramin, and, altered P2 receptor expression. This data suggests that increased ATP release from the urothelium, involving activation of P2 receptors, may play a role in the heightened symptoms associated with pyuric OAB patients.

Where applicable, experiments conform with Society ethical requirements