Urea modifies the permeability of the mammalian urothelium.

PURPOSE

This study investigated the effects of mucosal (urine side) and serosal (blood side) urea on the permeability properties of the in vitro mammalian urinary bladder epithelium.

MATERIALS AND METHODS

The permeability properties of the rabbit urinary bladder epithelium were studied in modified Ussing chambers using electrophysiological techniques.

RESULTS

Addition of two molar urea to the mucosal solution did not cause a significant change in the short circuit current (Isc, a measure of the ion transport capacity of the epithelium), or the transepithelial conductance (Gt, a measure of the ability of ions to diffuse across the epithelium). In contrast, addition of 0.5 M urea to the serosal solution caused an increase in Gt of approximately 35 microS/cm.2 as well as an increase in Isc over a 5 minute period. The site of the conductance increase by short-term serosal urea was at the apical membrane and not at the tight junctions. The urea-induced conductance completely reversed upon removal of urea, was non-selective, and the magnitude was voltage dependent. Long term serosal urea (greater than 30 minutes) resulted in an irreversible increase in transepithelial conductance. Mucosal urea altered the time course but not the magnitude of the serosal urea-induced conductance.

CONCLUSIONS

The ion permeability of the mammalian urinary bladder is increased by serosal urea. At short times the increase is at the apical membrane, while at long times the increase is at the tight junctions. The presence of mucosal urea slows the loss of urothelial barrier function caused by serosal urea.