title: Characterisation of the contractile dynamics of the resting ex vivo urinary bladder of the pig.
abstract: OBJECTIVE
  To characterise the area and movements of ongoing spontaneous localised contractions in the resting porcine urinary bladder and relate these to ambient intravesical pressure (Pves ), to further our understanding of their genesis and role in accommodating incoming urine.
  
  
  METHODS
  We used image analysis to quantify the areas and movements of discrete propagating patches of contraction (PPCs) on the anterior, anterolateral and posterior surfaces of the urinary bladders of six pigs maintained ex vivo with small incremental increases in volume. We then correlated the magnitude of Pves and cyclic changes in Pves with parameters derived from spatiotemporal maps.
  
  
  RESULTS
  Contractile movements in the resting bladder consisted only of PPCs that covered around a fifth of the surface of the bladder, commenced at various sites, and were of ≈6 s in duration. They propagated at around 6 mm/s, mainly across the anterior and lateral surface of the bladder by various, sometimes circular, routes in a quasi-stable rhythm, and did not traverse the trigone. The frequencies of these rhythms were low (3.15 cycles/min) and broadly similar to those of cyclic changes in Pves (3.55 cycles/min). Each PPC was associated with a region of stretching (positive strain rate) and these events occurred in a background of more constant strain. The amplitudes of cycles in Pves and the areas undergoing PPCs increased after a sudden increase in Pves but the frequency of cycles of Pves and of origin of PPCs did not change. Peaks in Pves cycles occurred when PPCs were traversing the upper half of the bladder, which was more compliant. The velocity of propagation of PPCs was similar to that of transverse propagation of action potentials in bladder myocytes and significantly greater than that reported in interstitial cells. The size of PPCs, their frequency and their rate of propagation were not affected by intra-arterial dosage with tetrodotoxin or lidocaine.
  
  
  CONCLUSIONS
  The origin and duration of PPCs influence both Pves and cyclic variation in Pves . Hence, propagating rather than stationary areas of contraction may contribute to overall tone and to variation in Pves . Spatiotemporal mapping of PPCs may contribute to our understanding of the generation of tone and the basis of clinical entities such as overactive bladder, painful bladder syndrome and detrusor overactivity.
authors: Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand.
authors: Roger G
authors: RG
authors: Lentle
authors: Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand.
authors: Gordon W
authors: GW
authors: Reynolds
authors: Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand.
authors: Patrick W M
authors: PW
authors: Janssen
authors: Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand.
authors: Corrin M
authors: CM
authors: Hulls
authors: Division of Urology, Palmerston North Hospital, Palmerston North, New Zealand.
authors: Quinten M
authors: QM
authors: King
authors: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
authors: John Paul
authors: JP
authors: Chambers
mesh_terms: D000818:Animals; D005260:Female; D007091:Image Processing, Computer-Assisted; D008012:Lidocaine / Q000494:pharmacology; D009116:Muscarine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011312:Pressure; D034421:Sus scrofa; D013552:Swine; D013779:Tetrodotoxin / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*; D014741:Video Recording
chemical_list: D013779:Tetrodotoxin; D009116:Muscarine; D008012:Lidocaine
keywords: bladder tone; contractile sequence; spatiotemporal mapping