Nielsen S, Chou C L, Marples D, Christensen E I, Kishore B K, Knepper M A
Department of Cell Biology, University of Aarhus, Denmark.
Proc Natl Acad Sci U S A. 1995 Feb 14;92(4):1013-7. doi: 10.1073/pnas.92.4.1013.
Water excretion by the kidney is regulated by the peptide hormone vasopressin. Vasopressin increases the water permeability of the renal collecting duct cells, allowing more water to be reabsorbed from collecting duct urine to blood. Despite long-standing interest in this process, the mechanism of the water permeability increase has remained undetermined. Recently, a molecular water channel (AQP-CD) has been cloned whose expression appears to be limited to the collecting duct. Previously, we immunolocalized this water channel to the apical plasma membrane (APM) and to intracellular vesicles (IVs) of collecting duct cells. Here, we test the hypothesis that vasopressin increases cellular water permeability by inducing exocytosis of AQP-CD-laden vesicles, transferring water channels from IVs to APM. Rat collecting ducts were perfused in vitro to determine water permeability and subcellular distribution of AQP-CD in the same tubules. The collecting ducts were fixed for immunoelectron microscopy before, during, and after exposure to vasopressin. Vasopressin exposure induced increases in water permeability and the absolute labeling density of AQP-CD in the APM. In parallel, the APM:IV labeling ratio increased. Furthermore, in response to vasopressin withdrawal, AQP-CD labeling density in the APM and the APM:IV labeling ratio decreased in parallel to a measured decrease in osmotic water permeability. We conclude that vasopressin increases the water permeability of collecting duct cells by inducing a reversible translocation of AQP-CD water channels from IVs to the APM.
肾脏的水排泄受肽类激素抗利尿激素调节。抗利尿激素可增加肾集合管细胞的水通透性，使更多水分从集合管尿液重吸收进入血液。尽管人们长期以来一直关注这一过程，但水通透性增加的机制仍未明确。最近，一种分子水通道（AQP-CD）已被克隆，其表达似乎仅限于集合管。此前，我们已通过免疫定位将这种水通道定位于集合管细胞的顶端质膜（APM）和细胞内囊泡（IVs）。在此，我们检验如下假设：抗利尿激素通过诱导载有AQP-CD的囊泡胞吐作用，将水通道从IVs转移至APM，从而增加细胞的水通透性。对大鼠集合管进行体外灌注，以测定同一肾小管中AQP-CD的水通透性和亚细胞分布。在暴露于抗利尿激素之前、期间和之后，将集合管固定用于免疫电子显微镜检查。暴露于抗利尿激素可导致水通透性增加以及APM中AQP-CD的绝对标记密度增加。同时，APM:IV标记比率增加。此外，抗利尿激素撤除后，APM中AQP-CD的标记密度和APM:IV标记比率下降，与测得的渗透水通透性下降平行。我们得出结论，抗利尿激素通过诱导AQP-CD水通道从IVs至APM的可逆转运，增加集合管细胞的水通透性。
