¹Laboratory of Epithelial Cell Biology and Renal-Electrolyte Division of the Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA

Correspondence: G Apodaca, University of Pittsburgh, Renal Division, 980 Scaife Hall, 3550 Terrace Street, Pittsburgh, Pennsylvania 15261, USA. E-mail: gla6@pitt.edu

Received 7 June 2007; Accepted 12 June 2007; Published online 1 August 2007.

Abstract

An important, but not well understood, function of epithelial cells is their ability to sense changes in their extracellular environment and then communicate these changes to the underlying nervous, connective, and muscular tissues. This communication is likely to be important for tube- and sac-shaped organs such as blood vessels, the lungs, the gut, and the bladder, whose normal function can be modulated by stimuli initiated within the epithelium. We propose that the uroepithelium, which lines the renal pelvis, ureters, and inner surface of the bladder, functions as an integral part of a 'sensory web.' Through uroepithelial-associated channels and receptors, the uroepithelium receives sensory 'inputs' such as changes in hydrostatic pressure and binding of mediators including adenosine triphosphate (ATP). These input signals stimulate membrane turnover in the outermost umbrella cell layer and release of sensory 'outputs' from the uroepithelium in the form of neurotransmitters and other mediators that communicate changes in the uroepithelial milieu to the underlying tissues, altering their function. The global consequence of this sensory web is the coordinated function of the bladder during the cycles of filling and voiding, and disruption of this web is likely to lead to bladder dysfunction.