Aims To test the hypothesis that vasopressin-sensitive aquaporin 2 (AQP2) may be present in the human urothelium and contribute towards obtaining night time continence.
Background In studies comparing dry and wet nights in children with enuresis it was hypothesised that there may be water transfer across the urothelium overnight resulting in an increase in urine concentration and a reduction in urine volume. The authors postulated that human urothelium would have to express the vasopressin receptor and AQP2.
Methods Using previously evaluated techniques, human urothelium was isolated and used to prepare messenger RNA, perform immunohistological studies and to establish finite NHU cell lines. All samples were then studied for expression of vasopressin receptor and aquaporins 0–12.
Results Native and cultured urothelia were negative for vasopressin receptor and AQP2 transcripts, whereas transcripts for aquaporins 3, 4, 7, 9 and 11 were detected. Immunohistochemistry revealed human urothelium to be intensely positive for AQP3 in the basal and intermediate layers of the urothelium, localising to intercellular borders. AQP 4 and 7 showed less intense cytoplasmic expression throughout the urothelium. No immunoreactivity was found for AQP 9.
Conclusion The original hypothesis that water transfer might occur across human urothelium due to the presence of vasopressin-sensitive AQP2 is incorrect. The detection of AQP 3 and 4 raises the possibility that water and urea transfer may occur across the urothelium. However, it is yet to be determined whether these proteins contribute to urinary continence mechanisms.