Osmosensing mechanism of co-operation of Nax and TRPV4 channel

TRPV4首次被报道为一种“低摩尔感测”阳离子通道。在接下来对敲除小鼠（Trpv4^<-/->）的研究中，我们报道了抗利尿激素对高渗性的反应被夸大，但另一组报道了抗利尿激素在Trpv4^<-/->中被消除。尽管在反应中存在争议，但两份报告都表明TRPV4可能对高渗刺激有反应。为了阐明TRPV4激活中的“高渗透压感应”，我们设计了在体内重新检查反应，并研究TRPV4在培养的神经细胞中是否对高渗透压敏感。Trpv4^<-/->和Trpv4^<+/+>小鼠脱水24 ~ 96小时。然后测定血浆渗透压和摄水量。血浆渗透压在各脱水时期无显著差异，但在脱水72 h时血浆渗透压Trpv4^<-/->显著降低。脱水后的渴求水行为和饮水量没有改变。因此，TRPV4通道可能对高渗透压有反应。以Neuro2a细胞系为基础，建立TRPV4和Nax表达和不表达的神经元细胞系。高渗透性（400mosm）在TRPV4（+）细胞中诱导了强大的Ca内流，而不考虑Nax的存在，而在TRPV4（-）细胞中则没有。吲哚美辛不能改变静脉内流，染料木素、咪康唑能部分阻断静脉内流，pa_2阻滞剂pBPB能完全阻断静脉内流。因此，TRPV4是通过激活PLA_2在神经元细胞中的高渗透压感知通道。

TRPV4 was first reported to be a "hypoosmolality-sensing" cation channel. On the following studies with knockout mice(Trpv4^<-/->), we have reported that response of vasopressin to hypertonicity was exaggerated but another group has reported that it was abolished in Trpv4^<-/->. Although controversial in the response, both reports suggest that TRPV4 can be responsive to hypertonic stimuli. To elucidate "hyperosmolality- sensing" in TRPV4 activation, we designed to re-examine the response in vivo and investigate whether TRPV4 was sensitive to hyperosmolality in cultured neuronal cells. Trpv4^<-/->and Trpv4^<+/+> mice were subjected to dehydration from 24 to 96 hrs. Then plasma osmolality and water intake were measured. There was not remarkable difference in plasma osmolality at any period of dehydration but a significant decrease in plasma osmolality of Trpv4^<-/-> at 72 hrs dehydration. Water-crave behavior and amount of water intakes after the dehydrations were not changed. Thus TRPV4 channel may respond to hyperosmolality. Neuronal cell lines with and without TRPV4 and Nax expression were established from the Neuro2a cell line. Hyperosmoliality(400 mOsm)induced robust Ca influx in the TRPV4(+) cells, irrespective of the presence of Nax, while not in the TRPV4(-)cells. The influx was not modified with indomethacin, partially blocked with genistein, miconazole, and completely blunted with pBPB, a blocker of PLA_2. Therefore, TRPV4 is hyperosmolality-sensng channel through activation of PLA_2 in the neuronal cells.