Mechanisms mediating osmoreception: Sustained response in the tilapia cell model

介导渗透感受的机制：罗非鱼细胞模型中的持续反应

• 批准号: 0517769
• 负责人: E. Gordon Grau
• 金额: --
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-10-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0517769&HistoricalAwards=false
• 关键词: Mechanisms; mediating; osmoreception; Sustained; response

Osmoregulation is fundamental to life in complex organisms. The structure and function of molecules that control the processes of life are maintained by weak forces (hydrophobic interactions and hydrogen bonds) and thus are sensitive to small changes in their ionic and osmotic environment. For this reason, organisms invest considerable energy in controlling intracellular and extracellular fluids. In fish, for example, osmoregulation typically consumes 25-50% of total metabolic output. Beyond this, osmotic equilibrium is a fragile balance that is maintained through the continuous interplay of a major portion of the neuroendocrine array. Indeed, a persistently difficult challenge in clinical medicine is the regulation of salt and water balance in seriously ill patients. In view of the cost and importance of osmoregulation, it may seem ironic that the mechanisms that monitor and control salt and water balance in vertebrates are so poorly understood. Closer attention, however, reveals the impediment: the typically complex structure and arrangement of osmoreceptive cells and tissues. In virtually all cases, one cannot simultaneously measure changes in cell size and the osmoregulatory output (hormone release) in a cell that can be distinguished specifically as osmoreceptive cells. In teleost fish, prolactin (PRL) is an essential osmoregulatory hormone that maintains hydromineral balance in fresh water and whose secretion is controlled directly by extracellular osmolality. Consistent with these actions, plasma PRL is elevated in the tilapia, Oreochromis mossambicus, a euryhaline teleost, in fresh water and PRL release is stimulated when extracellular osmolality declines. Our previous NSF-supported studies demonstrated that a fall in extracellular osmolality leads to the passive influx of water into the PRL cell that increases cell volume within minutes. This initiates an influx of extracellular Ca2+ through stretch-activated channels, producing a rise in intracellular calcium [Ca2+]i which stimulates PRL release. This rapid response is extended under sustained stimulation in vitro with increased PRL release being observed for 24 h in hyposmotic medium. On the other hand, PRL release is reduced under hyperosmotic conditions, reflecting its counteraction to salt water osmoregulation. However, signal transduction mechanisms that underlie the osmotic control of sustained PRL release and gene expression are not known. In fact, very little is known about the cellular mechanisms that transduce either acute or chronic osmotic information in any osmoregulatory endocrine system. The present work is aimed at characterizing cellular mechanisms by which extended exposure to physiological changes in ambient osmolality evoke sustained changes in PRL release and gene expression using the tilapia PRL cell model. These studies will provide new insight into the cell-signaling mechanisms that mediate the sustained alteration of the release and production of osmoregulatory hormones that at present cannot be obtained with other model systems. This work will involve students at many levels from high school to graduate students, including several underrepresented minorities, who will be trained in an important area of research, which will have an impact in cell physiology.

渗透调节是复杂生物体生命的基础。 控制生命过程的分子的结构和功能由弱力（疏水相互作用和氢键）维持，因此对其离子和渗透环境的微小变化敏感。 因此，生物体投入大量能量来控制细胞内和细胞外液。 例如，在鱼类中，渗透压调节通常消耗总代谢输出的 25-50%。 除此之外，渗透平衡是一种脆弱的平衡，通过神经内分泌阵列主要部分的持续相互作用来维持。 事实上，临床医学中持续存在的困难挑战是重病患者​​的盐和水平衡的调节。 考虑到渗透调节的成本和重要性，我们对脊椎动物中监测和控制盐和水平衡的机制知之甚少，这似乎很讽刺。 然而，更仔细的关注揭示了其中的障碍：渗透感受细胞和组织的典型复杂结构和排列。 几乎在所有情况下，人们都无法同时测量细胞大小的变化和可专门区分为渗透感受细胞的细胞的渗透调节输出（激素释放）。 在硬骨鱼中，催乳素（PRL）是一种重要的渗透压调节激素，可维持淡水中的水矿物质平衡，其分泌直接受细胞外渗透压控制。 与这些作用一致的是，罗非鱼、莫桑比克罗非鱼（Oreochromis mossambicus）（一种广盐硬骨鱼）的血浆 PRL 在淡水中升高，并且当细胞外渗透压下降时，PRL 释放受到刺激。 我们之前 NSF 支持的研究表明，细胞外渗透压的下降会导致水被动流入 PRL 细胞，从而在几分钟内增加细胞体积。 这会引发细胞外 Ca2+ 通过拉伸激活的通道流入，导致细胞内钙 [Ca2+]i 增加，从而刺激 PRL 释放。 这种快速反应在体外持续刺激下得到延长，在低渗介质中观察到 PRL 释放增加 24 小时。 另一方面，在高渗条件下，PRL 释放减少，反映了其对盐水渗透调节的反作用。 然而，PRL 持续释放和基因表达的渗透控制背后的信号转导机制尚不清楚。 事实上，人们对渗透调节内分泌系统中转导急性或慢性渗透信息的细胞机制知之甚少。 目前的工作旨在使用罗非鱼 PRL 细胞模型来表征细胞机制，通过这种机制，长期暴露于环境渗透压的生理变化会引起 PRL 释放和基因表达的持续变化。 这些研究将为介导渗透调节激素释放和产生持续改变的细胞信号传导机制提供新的见解，而目前其他模型系统无法获得这种机制。这项工作将涉及从高中到研究生的多个级别的学生，包括几个代表性不足的少数族裔，他们将在一个重要的研究领域接受培训，这将对细胞生理学产生影响。