Role of the urothelium in bladder function.

Historically, the urinary bladder urothelium has been viewed as a passive barrier; however, recent evidence has demonstrated that the urothelium is a responsive structure, which exhibits both "sensor" (i.e. ability to respond to thermal, mechanical and chemical stimuli) and "transducer" (i.e. ability to release chemicals) functions. Studies have also revealed that afferent nerves and urothelial cells in the bladder exhibit a number of common properties, including the expression of certain receptors and ion channels (i.e. vanilloid receptor-1). In addition, localization of afferent nerves adjacent to the urothelium suggests that these cells may be targets for transmitter release from bladder nerves or that chemicals released by urothelial cells may alter afferent excitability. Taken together, these and other findings suggest that alterations in afferents or epithelial cells in pelvic viscera may contribute to the sensory abnormalities in a number of pelvic disorders.