Mechanisms mediating osmoreception: Sustained response in the tilapia cell model

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，因此对离子和渗透环境的微小变化敏感。 出于这个原因，生物体在控制细胞内和细胞外液方面投入了相当大的能量。 例如，在鱼类中，代谢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的主要部分的持续相互作用来维持。 事实上，临床医学中的一个持续困难的挑战是重病患者的盐和水平衡的调节。 考虑到盐调节的成本和重要性，对脊椎动物中监测和控制盐和水平衡的机制知之甚少似乎有点讽刺意味。 然而，更仔细的观察揭示了障碍：典型的复杂结构和组织的细胞和组织的排列。 在几乎所有的情况下，人们不能同时测量细胞大小的变化和细胞中的激素调节输出（激素释放），这些细胞可以被特异性地区分为激素受体细胞。 在硬骨鱼中，催乳素（PRL）是维持淡水中水矿物质平衡的一种必需的哺乳动物调节激素，其分泌直接受细胞外渗透压的控制。 与这些行动相一致，血浆PRL升高的罗非鱼，Oreochromis mossambicus，广盐硬骨鱼，在淡水和PRL释放刺激时，细胞外渗透压下降。 我们以前的NSF支持的研究表明，细胞外渗透压的下降导致水被动流入PRL细胞，在几分钟内增加细胞体积。 这通过牵张激活的通道启动细胞外Ca 2+的流入，产生细胞内钙[Ca 2 +]i的升高，其刺激PRL释放。 这种快速反应在体外持续刺激下延长，在低渗培养基中观察到PRL释放增加24小时。 另一方面，PRL的释放在高渗条件下减少，反映了其对盐水调节的反作用。 然而，信号转导机制的基础上持续PRL释放和基因表达的渗透控制是未知的。 事实上，很少有人知道的细胞机制，无论是急性或慢性渗透信息在任何神经调节内分泌系统。 本工作的目的是表征细胞机制，延长暴露于环境渗透压的生理变化引起持续的变化，在催乳素释放和基因表达的罗非鱼PRL细胞模型。 这些研究将提供新的见解细胞信号传导机制，介导的持续改变的释放和生产的激素，目前不能获得与其他模型系统。这项工作将涉及从高中到研究生的许多层次的学生，包括几个代表性不足的少数民族，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。

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.