The human bladder urothelium: new concepts and future perspectives

The bladder urothelium has long been considered as having a purely passive role by providing a barrier protecting the underlying smooth muscle from irritative substances stored in the urine. Recent reports support the idea that urothelial cells represent more than a protective layer. They exhibit a number of dynamic sensory properties that allow them to respond to either chemical and physical environments. These properties include the expression of nicotinic, muscarinic, tachykinin and adrenergic receptors, as well as vanilloid receptors. Furthermore, urothelial cells exhibit responsiveness to some neurotransmitters (ATP, NKA, Substance P) released from afferent nerves, and they are able to release chemical mediators such as ATP and NO, which regulate the activity of underlying nerves. Moreover, the concept that the bladder urothelium can participate in non-barriers functions is supported by the recent observation that in some species, this tissue produces and releases proteolytic enzymes.