Koyama Y, Yamamoto T, Tani T, Nihei K, Kondo D, Funaki H, Yaoita E, Kawasaki K, Sato N, Hatakeyama K, Kihara I
1st Department of Surgery, Niigata University School of Medicine, 1-757 Asahimachi-dori, Niigata 951-8510, Japan.
Am J Physiol. 1999 Mar;276(3):C621-7. doi: 10.1152/ajpcell.1999.276.3.C621.
A family of water-selective channels, aquaporins (AQP), has been demonstrated in various organs and tissues. However, the localization and expression of the AQP family members in the gastrointestinal tract have not been entirely elucidated. This study aimed to demonstrate the expression and distribution of several types of the AQP family and to speculate on their role in water transport in the rat gastrointestinal tract. By RNase protection assay, expression of AQP1-5 and AQP8 was examined in various portions through the gastrointestinal tract. AQP1 and AQP3 mRNAs were diffusely expressed from esophagus to colon, and their expression was relatively intense in the small intestine and colon. In contrast, AQP4 mRNA was selectively expressed in the stomach and small intestine and AQP8 mRNA in the jejunum and colon. Immunohistochemistry and in situ hybridization demonstrated cellular localization of these AQP in these portions. AQP1 was localized on endothelial cells of lymphatic vessels in the submucosa and lamina propria throughout the gastrointestinal tract. AQP3 was detected on the circumferential plasma membranes of stratified squamous epithelial cells in the esophagus and basolateral membranes of cardiac gland epithelia in the lower stomach and of surface columnar epithelia in the colon. However, AQP3 was not apparently detected in the small intestine. AQP4 was present on the basolateral membrane of the parietal cells in the lower stomach and selectively in the basolateral membranes of deep intestinal gland cells in the small intestine. AQP8 mRNA expression was demonstrated in the absorptive columnar epithelial cells of the jejunum and colon by in situ hybridization. These findings may indicate that water crosses the epithelial layer through these water channels, suggesting a possible role of the transcellular route for water intake or outlet in the gastrointestinal tract.
水通道蛋白（AQP）家族是一类水选择性通道，已在各种器官和组织中得到证实。然而，AQP家族成员在胃肠道中的定位和表达尚未完全阐明。本研究旨在证明几种类型的AQP家族的表达和分布，并推测它们在大鼠胃肠道水转运中的作用。通过核糖核酸酶保护试验，检测了胃肠道各部位AQP1-5和AQP8的表达。AQP1和AQP3的信使核糖核酸从食管到结肠呈弥漫性表达，在小肠和结肠中的表达相对较强。相比之下，AQP4信使核糖核酸在胃和小肠中选择性表达，AQP8信使核糖核酸在空肠和结肠中表达。免疫组织化学和原位杂交显示了这些AQP在这些部位的细胞定位。AQP1定位于整个胃肠道黏膜下层和固有层淋巴管的内皮细胞上。在食管分层鳞状上皮细胞的周质膜上、胃下部贲门腺上皮细胞的基底外侧膜上以及结肠表面柱状上皮细胞的基底外侧膜上检测到AQP3。然而，在小肠中未明显检测到AQP3。AQP4存在于胃下部壁细胞的基底外侧膜上，并选择性地存在于小肠深部肠腺细胞的基底外侧膜上。原位杂交显示AQP8信使核糖核酸在空肠和结肠的吸收性柱状上皮细胞中表达。这些发现可能表明水通过这些水通道穿过上皮层，提示在胃肠道中跨细胞途径在水摄入或排出中可能发挥的作用。
