Proceedings of The Physiological Society

Physiology 2015 (Cardiff, UK) (2015) Proc Physiol Soc 34, PC271

Poster Communications

Spreading of micromotions in juvenile rat bladder: directionality and function of gap junctions

D. A. Bijos1, M. J. Drake1,2

1. School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom. 2. Bristol Urological Institute, NHS North Bristol Trust, Bristol, United Kingdom.

Urinary bladders display spontaneous phasic activity manifested as pressure fluctuations and bladder wall movements i.e. micromotions. Phasic activity is pronounced in bladders of young animals and changes during ageing. These changes give insight into factors moderating such activity, which could be relevant in the clinical context e.g. for overactive bladder syndrome. Hence, here we characterise the effects of 18β-glycyrrhetinic acid (18β-GA), a known gap junction blocker, on whole organ pressure fluctuations and bladder wall micromotions. Methods: 3 week old (21±2 days) Wistar rats were killed by UK Schedule 1 procedures (N=15). Bladders were dissected and catheterized with 26GA venflon (Becton Dickinson), filled with ~350µl Krebs (NaCl 118.4mM, glucose 11.7mM, NaHCO3 24.9mM, KCl 4.7mM, CaCl2 1.9mM, MgSO4 1.15mM, KH2PO4 1.15mM) and carbon particles were applied to the bladder surface to monitor movements. Bladders were placed in an oxygenated organ bath (150ml) in Krebs solution at 37°C. Pressure and video data were simultaneously acquired at 10Hz via LabView application (National Instruments, USA) and a camera (Prosilica EC650). After at least 30min of equilibration in isovolumetric conditions, 30μM 18β-GA was administered (or 0.1% DMSO as a drug vehicle control). We compared 5 minute periods before and after drug addition using a two-tailed paired Student's t-test (GraphPad Prism) and calculated percentage change of each parameter. Distances between the carbon points on the bladder wall were analysed (LabView) and plotted in LabChart (ADInstruments). Results: 18β-GA decreased spontaneous phasic pressure fluctuations: the amplitude decreased by 79.8% (N=6) (p<0.001). When pressure fluctuations were detectable the frequency remained unchanged (3/6). Movement of bladder wall persisted at 30 minutes after addition of 18β-GA in all preparations, including three experiments without detectable pressure changes (<1cmH2O). Quantification of distances between points on the bladder wall confirmed altered pattern of movement with 18β-GA. Not all pressure fluctuations could be explained by visualised movement: distance elongations and shortenings coincided with pressure fluctuation changes, but not all rhythmical micromotions were synchronous with pressure change. This suggests that rhythmicity of localised movements on bladder wall is independent of pressure fluctuation. Longitudinal distances showed a dynamic pattern of contractions, where one part was contracting before the other, suggesting dynamic propagation of movement in this direction. Conclusions: In general, in spontaneously active whole bladder the movements started at the top of the bladder dome and bladder base and spreading vertically (longitudinally). Gap junctions change but do not block bladder wall movements.

Where applicable, experiments conform with Society ethical requirements