Ma T, Yang B, Verkman A S
Department of Medicine, University of California, San Francisco 94143-0521, USA.
Biochem Biophys Res Commun. 1997 Nov 17;240(2):324-8. doi: 10.1006/bbrc.1997.7664.
An aquaporin-type water channel was isolated from mouse based on homology to known aquaporins. A 1447 bp cDNA was sequenced (designated AQP8) with a 783 bp open reading frame encoding a 261 amino acid hydrophobic protein which contained the conserved NPA motifs of MIP family members. Amino acid alignment showed greatest homology of AQP8 to plant water channel gamma TIP (38% identity) followed by mammalian water channels AQP4 (32%) and AQP2 (31%). Northern blot analysis indicated a 1.7 kb transcript expressed strongly in placenta > colon > liver approximately heart. RT-PCR with AQP8-specific primers and Southern blot analysis showed AQP8 transcript in the above tissues and in pancreas, lung, kidney, submandibular gland, diaphragm, testis, spleen, stomach and brain. Expression of AQP8 cRNA in Xenopus oocytes increased osmotic water permeability from (0.8 +/- 0.1) x 10(-3) cm/s to (22 +/- 3) x 10(-3) cm/s (10 degrees C) in a mercurial-sensitive manner. AQP8 was also permeable to urea but not to glycerol. Normalization for oocyte plasma membrane expression using cMyc-tagged AQP8 indicated a single channel water permeability of 8.2 x 10(-14) cm3/s. AQP8 is unique among the water channels in terms of its urea permeability and its strong expression in gastrointestinal organs, placenta and heart.
基于与已知水通道蛋白的同源性，从小鼠中分离出一种水通道蛋白类型的水通道。对一个1447 bp的cDNA进行了测序（命名为AQP8），其开放阅读框为783 bp，编码一个261个氨基酸的疏水蛋白，该蛋白包含MIP家族成员保守的NPA基序。氨基酸序列比对显示，AQP8与植物水通道蛋白γ-TIP的同源性最高（同一性为38%），其次是哺乳动物水通道蛋白AQP4（32%）和AQP2（31%）。Northern印迹分析表明，在胎盘中表达强烈的1.7 kb转录本在结肠、肝脏中的表达量大致与心脏相当。用AQP8特异性引物进行RT-PCR和Southern印迹分析表明，上述组织以及胰腺、肺、肾、下颌下腺、膈肌、睾丸、脾脏、胃和脑中均有AQP8转录本。在非洲爪蟾卵母细胞中表达AQP8的cRNA，以汞敏感的方式使渗透水通透性从(0.8±0.1)×10(-3) cm/s增加到(22±3)×10(-3) cm/s（10℃）。AQP8也可通透尿素，但不通透甘油。使用带有cMyc标签的AQP8对卵母细胞质膜表达进行标准化后，表明单通道水通透性为8.2×10(-14) cm3/s。就尿素通透性及其在胃肠道器官、胎盘和心脏中的强表达而言，AQP8在水通道中是独特的。
