The bladder epithelium and overactive bladder: what we know.

Although the urothelium has been traditionally thought of as a passive barrier between urine and detrusor muscle, new studies have shown that the urothelium is a highly specialized structure involved in antigen presentation, micturition reflex, metabolic secretion, inflammatory regulation, and sensory afferent functioning. Data from several laboratories have shown that the urothelium can respond to thermal, mechanical, and chemical stimuli. The earlier findings (activation of urothelial transient receptor potential channel vanilloid 1 producing the second messenger nitric oxide, which in turn triggers suburothelial sensory nerves) demonstrate how the urothelium acts as a transducer, releasing chemicals that target adjacent bladder cells and sensory neurons. We now know that bladder urothelium acts also as a transducer whereby afferent neurons, via urothelial mechanoafferent transduction, are involved in the micturition process and the pathogenesis of bladder disorders. This paper highlights the important role that the urothelium has in bladder pathophysiology.