Lewis S A, Kleine T J
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston Texas 77555-0641, USA.
J Urol. 2000 Jul;164(1):219-23.
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.
The permeability properties of the rabbit urinary bladder epithelium were studied in modified Ussing chambers using electrophysiological techniques.
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.
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.
本研究调查了黏膜侧（尿液侧）和浆膜侧（血液侧）尿素对体外哺乳动物膀胱上皮通透性的影响。
采用电生理技术，在改良的Ussing室中研究兔膀胱上皮的通透性。
向黏膜溶液中添加两摩尔尿素，并未使短路电流（Isc，上皮离子转运能力的一种度量）或跨上皮电导（Gt，离子跨上皮扩散能力的一种度量）发生显著变化。相比之下，向浆膜溶液中添加0.5 M尿素会使Gt在5分钟内增加约35 μS/cm²，同时Isc也增加。短期浆膜侧尿素导致的电导增加部位在顶端膜而非紧密连接。去除尿素后，尿素诱导的电导完全逆转，具有非选择性，且其大小依赖于电压。长期浆膜侧尿素（超过30分钟）导致跨上皮电导不可逆增加。黏膜侧尿素改变了浆膜侧尿素诱导电导的时间进程，但未改变其大小。
浆膜侧尿素可增加哺乳动物膀胱的离子通透性。短时间内增加发生在顶端膜，长时间则发生在紧密连接。黏膜侧尿素的存在减缓了浆膜侧尿素导致的尿路上皮屏障功能丧失。
