Sabolić I, Katsura T, Verbavatz J M, Brown D
Renal Unit, Massachusetts General Hospital, Charlestown 02129, USA.
J Membr Biol. 1995 Feb;143(3):165-75. doi: 10.1007/BF00233445.
Aquaporin 2 is a collecting duct water channel that is located in apical vesicles and in the apical plasma membrane of collecting duct principal cells. It shares 42% identity with the proximal tubule/thin descending limb water channel, CHIP28. The present study was aimed at addressing three questions concerning the location and behavior of the AQP2 protein under different conditions. First, does the AQP2 channel relocate to the apical membrane after vasopressin treatment? Our results show that AQP2 is diffusely distributed in cytoplasmic vesicles in collecting duct principal cells of homozygous Brattleboro rats that lack vasopressin. In rats injected with exogenous vasopressin, however, AQP2 became concentrated in the apical plasma membrane of principal cells, as determined by immunofluorescence and immunogold electron microscopy. This behavior is consistent with the idea that AQP2 is the vasopressin-sensitive water channel. Second, is the cellular location of AQP2 modified by microtubule disruption? In normal rats, AQP2 has a mainly apical and subapical location in principal cells, but in colchicine-treated rats, it is distributed on vesicles that are scattered throughout the entire cytoplasm. This is consistent with the dependence on microtubules of apical protein targeting in many cell types, and explains the inhibitory effect of microtubule disruption on the hydroosmotic response to vasopressin in sensitive epithelia, including the collecting duct. Third, is AQP2 present in neonatal rat kidneys? We show that AQP2 is abundant in principal cells from neonatal rats at all days after birth. The detection of AQP2 in early neonatal kidneys indicates that a lack of this protein is not responsible for the relatively weak urinary concentrating response to vasopressin seen in neonatal rats.
水通道蛋白2是一种集合管水通道，位于集合管主细胞的顶端囊泡和顶端质膜中。它与近端小管/细降支水通道CHIP28有42%的同源性。本研究旨在解决关于水通道蛋白2（AQP2）蛋白在不同条件下的定位和行为的三个问题。第一，血管加压素处理后AQP2通道是否会重新定位到顶端膜？我们的结果表明，AQP2在缺乏血管加压素的纯合布拉特洛维大鼠的集合管主细胞的胞质囊泡中呈弥散分布。然而，通过免疫荧光和免疫金电子显微镜测定，在注射外源性血管加压素的大鼠中，AQP2集中在主细胞的顶端质膜中。这种行为与AQP2是血管加压素敏感水通道的观点一致。第二，微管破坏是否会改变AQP2的细胞定位？在正常大鼠中，AQP2在主细胞中主要位于顶端和亚顶端位置，但在秋水仙碱处理的大鼠中，它分布在散布于整个细胞质中的囊泡上。这与许多细胞类型中顶端蛋白靶向对微管的依赖性一致，并解释了微管破坏对包括集合管在内的敏感上皮细胞对血管加压素的水渗透反应的抑制作用。第三，新生大鼠肾脏中是否存在AQP2？我们表明，出生后所有天数的新生大鼠主细胞中AQP2都很丰富。在新生早期肾脏中检测到AQP2表明，这种蛋白的缺乏并不是新生大鼠对血管加压素的尿浓缩反应相对较弱的原因。
