Japan Society for the Promotion of Science, Tokyo, Japan.
Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan.
Cell Physiol Biochem. 2021 Mar 13;55(S1):119-134. doi: 10.33594/000000342.
BACKGROUND/AIMS: Arginine vasopressin (AVP) neurons play an important role for sensing a change in the plasma osmolarity and thereby responding with regulated AVP secretion in order to maintain the body fluid homeostasis. The osmo-sensing processes in magnocellular neurosecretory cells (MNCs) including AVP and oxytocin (OXT) neurons of the hypothalamus were reported to be coupled to sustained osmotic shrinkage or swelling without exhibiting discernible cell volume regulation. Since increasing evidence has shown some important differences in properties between AVP and OXT neurons, osmotic volume responses are to be reexamined with distinguishing these cell types from each other. We previously reported that AVP neurons identified by transgenic expression of enhanced green fluorescence protein (eGFP) possess the ability of regulatory volume decrease (RVD) after hypoosmotic cell swelling. Thus, in the present study, we examined the ability of regulatory volume increase (RVI) after hyperosmotic cell shrinkage in AVP neurons.
Here, we used eGFP-identified AVP neurons acutely dissociated from AVP-eGFP transgenic rats. We performed single-cell size measurements, cytosolic RT-PCR analysis, AVP secretion measurements, and patch-clamp studies.
The AVP neurons were found to respond to a hyperosmotic challenge with physiological cell shrinkage caused by massive secretion of AVP, called a secretory volume decrease (SVD), superimposed onto physical osmotic cell shrinkage, and also to exhibit the ability of RVI coping with osmotic and secretory cell shrinkage. Furthermore, our pharmacological and molecular examinations indicated that AVP secretion and its associated SVD event are triggered by activation of T-type Ca channels, and the RVI event is attained by parallel operation of Na/H exchanger and Cl/HCO anion exchanger.
Thus, it is concluded that AVP neurons respond to hyperosmotic stimulation with the regulatory volume increase and the secretory volume increase by activating ion transporters and Ca channels, respectively.
背景/目的：精氨酸加压素（AVP）神经元在感知血浆渗透压变化方面发挥着重要作用，通过调节 AVP 分泌来维持体液平衡。据报道，包括下丘脑大细胞神经分泌细胞（MNCs）中的 AVP 和催产素（OXT）神经元在内的渗透压感受器过程与持续的渗透压收缩或膨胀有关，而没有表现出明显的细胞体积调节。由于越来越多的证据表明 AVP 和 OXT 神经元在性质上存在一些重要差异，因此需要重新检查渗透压体积反应，以区分这些细胞类型。我们之前报道过，通过增强型绿色荧光蛋白（eGFP）转基因表达鉴定的 AVP 神经元在低渗细胞肿胀后具有调节性体积减少（RVD）的能力。因此，在本研究中，我们检查了 AVP 神经元在高渗细胞收缩后的调节性体积增加（RVI）能力。
在这里，我们使用从 AVP-eGFP 转基因大鼠急性分离的 eGFP 鉴定的 AVP 神经元。我们进行了单细胞大小测量、胞质 RT-PCR 分析、AVP 分泌测量和膜片钳研究。
发现 AVP 神经元对高渗刺激做出反应，导致大量 AVP 分泌引起的生理细胞收缩，称为分泌性体积减少（SVD），叠加在物理渗透压细胞收缩上，并且还表现出应对渗透压和分泌性细胞收缩的 RVI 能力。此外，我们的药理学和分子研究表明，AVP 分泌及其相关的 SVD 事件是通过激活 T 型钙通道触发的，而 RVI 事件是通过 Na/H 交换器和 Cl/HCO 阴离子交换器的并行操作实现的。
因此，结论是 AVP 神经元通过激活离子转运体和钙通道分别对高渗刺激做出调节性体积增加和分泌性体积增加的反应。
