The protective layer of the bladder: Is it mucin?
N'Dow JM., Pearson JP., Sunderland AM., Neal DE., Robson CN.
INTRODUCTION: The protective layer of the urinary tract is commonly referred to as the mucin coat or layer. There is as yet little evidence to support a substantial mucus layer. If there is a dynamic and functional mucus layer then mucin should be present in urine and it should also be easily detected on the bladder surface. We have studied pig bladders as the pig is a good model for man in other mucin secretory epithelium. MATERIALS AND METHODS: The mucosa of 100 pig bladders were scraped into a cocktail of protease inhibitors. 200ml of urine was also collected from 5 pig bladders. Samples were homogenised, centrifuged, desalted and freeze dried. They were then digested with papain at 60°C for 48hr, dialysed exhaustively, followed by Sephadex G-150 gel filtration on a 30 × 1.5 cm column. Eluted fractions were then assayed for glycoprotein by the Periodic Acid/Schiff (PAS) method. RESULTS: PAS positive material from 100 pig bladders amounted to 635.76mg. The average pig bladder surface area was 81.88cm: resulting in a total PAS positive material of 77.65ng/cm: pig bladder. Based on a mucin gel being 50mg/ml mucin, then the maximum thickness of a continuous layer that can be achieved with 77.65 μg/cm2 of PAS material is 15.6μm. Pig urine contained 0.285mg/ml PAS positive material of which only 5% had a mucin elution profile. CONCLUSION. It is unlikely a substantial continuous mucus layer exists in pig bladder and the very low levels of mucin-like material in the urine suggests that any mucin layer that does exist is only being turned over very slowly.