Molecular mechanisms of expression and regulation of water channel proteins aquaporins in the exocrine gland cells

研究了水通道蛋白5（AQP 5）在大鼠Brunner腺中的定位及血管活性肠肽（VIP）对其的调节作用。VIP在体外处理十二指肠切片2或7 min显著增加了十二指肠顶膜部分中AQP 5的量。静脉注射VIP（40 μ g/kg体重）2或7 min可引起管腔的强烈扩张，并增加顶膜和侧膜中AQP 5的染色强度，而细胞内部的染色明显减少。AQP 1也被发现定位于顶膜和基底外侧膜的Brunner腺，VIP，但没有引起任何显着的变化，AQP 1水平的顶膜判断的结果，在体外和体内实验。结果提示VIP可诱导Brunner腺颗粒物质的胞吐，并引起AQP 5向腺顶膜移位，且不同SD系大鼠颌下腺水通道蛋白（AQP）5的表达水平不同。这种差异被观察到的AQP 5，但不是AQP 1，因此SD株分为两组，一个表达高水平的AQP 5和其他一个低。在高表达和低表达鼠之间重复进行两次兄妹交配，获得第三代（F2），高表达鼠第三代（F2）SMG AQP 5水平显著高于低表达鼠F2。我们目前的研究表明，水通道蛋白，AQP 5，在大鼠的表达存在遗传变异。

Localization of aquaporin 5 (AQP5) in the rat Brunner's gland and its regulation by vasoactive intestinal polypeptide (VIP) were in vestigated. Treatment of slices of duodenum with VIP in vitro for 2 or 7 min significantly increased amount of AQP5 in the duodenal apical membrane fraction. Intravenous injection of rats with VIP (40 ug/kg body weight) for 2 or 7 min provoked strong dilation of the lumen and increased the staining intensity of AQP5 in the apical and lateral membranes,whereas thae staining inside of the cells was appreciably reduced. AQP1 was also found to be localized in the apical and basolateral membranes of Brunner's gland; VIP however did not provoke any significant change in the AQP1 level in the apical membrane as judged from the results of the in vitro and vivo experiments. These results suggest that VIP induced the exocytosis of granule contents and simultanenously caused translocation of AQP5 to the apical membrane in the Brunner's gland.The expression level of aquapoin (AQP)5 in the submandibular gland (SMG) was found to be different among individual rats of the Sprague-Dawley (SD) straim. Such differences were observed for AQP5 but not for AQP1 and consequently the SD strain was divided into two groups, one expressing a high level of AQP5 and the other a low one. Breeding between brother and sister was repeated for two times within high expressers and low expressers to obtain the third generation progenies (F2); the AQP5 level of the SMG in the third generation (F2rats) from high expressers was significantly higher than the F2 from low expressers. Our present study suggests the existence of genetic variation in the expression of a water channel protein, AQP5, in rats.