Regulated vesicle exocytosis is a key response to extracellular stimuli in diverse physiological processes; including hormone regulated short-term urine concentration. In the renal collecting duct, the water channel aquaporin-2 localizes to the apical plasma membrane as well as small, sub-apical vesicles. In response to stimulation with the antidiuretic hormone, arginine vasopressin, aquaporin-2 containing vesicles fuse with the plasma membrane, which increases collecting duct water reabsorption and thus, urine concentration. The nano-scale size of these vesicles has limited analysis of their 3D organization. Using a cell system combined with 3D super resolution microscopy, we provide the first direct analysis of the 3D network of aquaporin-2 containing exocytic vesicles in a cell culture system. We show that aquaporin-2 vesicles are 43 ± 3nm in diameter, a size similar to synaptic vesicles, and that one fraction of AQP2 vesicles localized with the sub-cortical F-actin layer and the other localized in between the F-actin layer and the plasma membrane. Aquaporin-2 vesicles associated with F-actin and this association was enhanced in a serine 256 phospho-mimic of aquaporin-2, whose phosphorylation is a key event in antidiuretic hormone-mediated aquaporin-2 vesicle exocytosis.

中文翻译：

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受调控的胞吐作用：肾水通道蛋白 2 3D 囊泡网络组织和与 F-肌动蛋白的关联

受调节的囊泡胞吐作用是多种生理过程中对细胞外刺激的关键反应；包括激素调节短期尿浓度。在肾集合管中，水通道 aquaporin-2 定位于顶端质膜以及小的亚顶端囊泡。响应抗利尿激素、精氨酸加压素、含有水通道蛋白 2 的囊泡与质膜的刺激，这会增加集合管对水的重吸收，从而增加尿液浓度。这些囊泡的纳米级尺寸对其 3D 组织的分析有限。使用细胞系统与 3D 超分辨率显微镜相结合，我们首次直接分析了细胞培养系统中含有胞外囊泡的水通道蛋白 2 的 3D 网络。我们发现水通道蛋白 2 囊泡的直径为 43 ± 3 nm，大小与突触囊泡相似，一部分 AQP2 囊泡位于皮层下 F-肌动蛋白层，另一部分位于 F-肌动蛋白层和质膜。水通道蛋白 2 囊泡与 F-肌动蛋白相关，这种关联在水通道蛋白 2 的丝氨酸 256 磷酸化模拟物中得到增强，其磷酸化是抗利尿激素介导的水通道蛋白 2 囊泡胞吐作用的关键事件。