Everything you wanted to know about the bladder epithelium but were afraid to ask

Abstract

The mammalian urinary bladder epithelium (urothelium) performs the important function of storing urine for extended periods, while maintaining the urine composition similar to that delivered by the kidneys. The urothelium possesses four properties to perform this function. First, it offers a minimum epithelial surface area-to-urine volume; this reduces the surface area for passive movement of substances between lumen and blood. Second, the passive permeability of the apical membrane and tight junctions is very low to electrolytes and nonelectrolytes. Third, the urothelium has a hormonally regulated sodium absorptive system; thus passive movement of sodium from blood to urine is countered by active sodium reabsorption. Last, the permeability properties of the apical membrane and tight junctions of the urothelium are not altered by most substances found in the urine or blood. The importance of the barrier function of the urothelium is illustrated by infectious cystitis. The loss of the barrier function results in the movement of urinary constituents into the lamina propria and underlying muscle layers, resulting in suprapubic and lower back pain and frequent, urgent, and painful voiding.

Vanilloid receptor expression suggests a sensory role for urinary bladder epithelial cells

“…To further evaluate expression within the urothelium at the protein level, sections of rat urinary bladder were processed for either VR1 or VRL-1 immunoreactivity (IR) by using specific polyclonal antisera. The urothelium is a multilayered structure consisting of basal cells, intermediate cells, and large superficial cells (9). Immunostaining revealed VR1-IR in both basal and superficial epithelial cells ( Fig.…”

Bacterial Penetration of Bladder Epithelium through Lipid Rafts

“…It is interesting that the typically noninvasive uropathogenic E. coli is able to invade the bladder epithelium, considering the highly impermeable barrier it presents to its luminal contents (12,13). It has been shown recently that the high impermeability of the urothelium arises largely from the presence of scallopshaped plaques on the apical surface of the superficial BEC, also known as the asymmetric unit membrane, which line the lumen of the bladder (13,14).…”

“…It has been shown recently that the high impermeability of the urothelium arises largely from the presence of scallopshaped plaques on the apical surface of the superficial BEC, also known as the asymmetric unit membrane, which line the lumen of the bladder (13,14). These plaques are composed of four subunits, known as uroplakins (UP): UPIa, the host receptor for type 1 fimbriated E. coli (15), and UPIb, which pair with UPII and UPIII, respectively (16).…”

Characterization of tight junction proteins in cultured human urothelial cells

“…The urothelium consists of basal, intermediate, and superficial cells lining the urinary tract from the renal pelvis to the proximal urethra (review, Lewis 2000). Superficial cells develop tight junctions (TJs) that restrict urine movement across the urothelium.…”