Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC118
Investigation of the role of icilin, a TRPM8 channel agonist, in mediation of detrusor contraction in pig urinary bladder
B. Vahabi1,2, B. A. Parsons2, M. J. Drake2
1. University of the West of England, Bristol, United Kingdom. 2. Bristol Urological Institute, Bristol, United Kingdom.
Transient receptor potential (TRP) channels have been shown to play an important role in the modulation of bladder sensation and afferent nerve activity. Recently a novel receptor, TRP melastatin 8 (TRPM8), activated by icilin and cool temperatures (8-28○C) has been identified in human bladders (1). The physiological and pathophysiological role of these channels remains unclear and few studies have investigated their function in mediating detrusor contraction (2). The aim of this study was to investigate the effect of icilin, a TRPM8 channel agonist, on strip and whole pig bladder contraction. Fresh female pig bladders were obtained from the local abattoir. For whole organ experiments, the bladder and the associated vasculature were excised and maintained under controlled physiological conditions, perfused with Krebs buffer. The effect of intravesical (IVE) or intravascular (IVA) administration of icilin (50µM) on carbachol-induced (10µM) whole bladder contractions was monitored by recording the IVE pressure (cmH2O). For isolated strip experiments, longitudinal strips of denuded detrusor or mucosa were mounted in Perspex microbaths, superfused with Krebs solution and maintained at 37○C. Strips were exposed to 10μM carbachol and once contractions had stabilised, 50µM icilin or vehicle were applied to the strips 10min before application of carbachol. All data are expressed as the mean±SEM. Statistical analysis was carried out by using repeated measure ANOVA followed by Dunett’s post hoc test. IVA administration of 50µM icilin significantly (p<0.05) decreased the magnitude of the carbachol-induced whole bladder (n=4) contraction as evidenced by reduced intravesical pressure rises (no icilin: 11.39±0.87 cmH2O vs. 50µM icilin: 9.60±1.12 cmH2O). In contrast, IVE administration (n=3) of 50µM icilin significantly (p<0.05) increased the carbachol-induced IVE pressure rise (no icilin: 13.71±2.05 cmH2O vs. 50µM icilin: 18.08±2.94 cmH2O). The carbachol-induced contractions of both detrusor (n=13) and mucosal (n=10) strips were also significantly inhibited by 50µM icilin (p<0.01 and p<0.05 respectively). The vehicle control had no effect on carbachol stimulated whole bladder or muscle strip contractions at all concentrations. Icilin appears to have the potential to modulate pig bladder contractility. Functional activation of TRPM8 channels in the whole organ resulted in different contractile responses depending on the route of icilin administration (IVE vs. IVA). However, consistent inhibitory responses were seen when strips of tissue (muscle & mucosa) were used. The differing smooth muscle responses seen with various routes of icilin administration may reflect regionalisation of mechanisms in different layers of the bladder wall.
Where applicable, experiments conform with Society ethical requirements