Verkman A S, Lencer W I, Brown D, Ausiello D A
Cardiovascular Research Institute, University of California, San Francisco 94143.
Nature. 1988 May 19;333(6170):268-9. doi: 10.1038/333268a0.
The mechanism by which vasopressin rapidly and dramatically increases the water permeability of target epithelial cell membranes is thought to involve a cycle of exo- and endocytosis during which vesicles carrying 'water channels' are successively inserted into, and removed from the apical plasma membrane of epithelial cells. Clusters of intramembranous particles, visible by freeze-fracture electron microscopy and presumed to represent water channels, appear on apical membranes in parallel with increased transepithelial water flow. In the collecting duct, these clusters are located in clathrin-coated pits which are subsequently internalized. There has been no direct evidence, however, that subcellular membranes in vasopressin-sensitive epithelia contain functional water channels. In this report, we have used fluorophores that are sensitive to volume and do not pass through membranes to label and to measure directly the osmotic water permeability of endocytosed vesicles isolated from renal papilla. We present direct evidence that vasopressin induces the appearance of a population of endocytic vesicles whose limiting membranes contain water channels.
血管加压素迅速且显著增加靶上皮细胞膜水通透性的机制，被认为涉及胞吐和胞吞循环，在此过程中，携带“水通道”的囊泡相继插入上皮细胞顶端质膜并从其移除。通过冷冻断裂电子显微镜可见的成簇膜内颗粒，推测代表水通道，其出现在顶端膜上的同时跨上皮水流量增加。在集合管中，这些簇位于网格蛋白包被的小窝中，随后被内化。然而，尚无直接证据表明血管加压素敏感上皮细胞中的亚细胞膜含有功能性水通道。在本报告中，我们使用了对体积敏感且不能透过膜的荧光团，来标记并直接测量从肾乳头分离的内吞囊泡的渗透水通透性。我们提供了直接证据，表明血管加压素可诱导出现一群内吞囊泡，其界膜含有水通道。
