Cell Volume Regulation in Bivalves: Response to Fluctuating Salinity

9407997赖特由于海水中盐的浓度非常高，海洋动物生活在持续的盐度压力下。海洋无脊椎动物通常通过在细胞中维持无机溶质的组合来应对这种压力，无机溶质的组合在一起平衡了全强度海水的大渗透浓度。河口无脊椎动物面临着一个额外的挑战。由于潮汐的每日变化，河口环境可以周期性地从充满活力的海水转变为淡水。因此，生活在潮间带栖息地的动物可能会暴露在环境渗透压的变化中，这可能对它们的生理产生深远的影响。特别是，当暴露于渗透压降低（即稀释的海水）时，河口动物的细胞和组织通常会膨胀。人们普遍认为，细胞对这种类型的压力的反应包括溶质的损失，从而引起渗透性的水分损失，从而使体积减少到正常水平。事实上，许多哺乳动物的细胞都是如此。对于渗透压每天变化很大的河口动物来说，当潮汐变化和环境渗透压恢复正常时，溶质的任何损失都必须由等量的溶质增加来弥补。虽然细胞溶质的这些循环损失和获得可能代表了动物的大量能量成本，但与暴露于循环相关的能量应激的实际程度是未知的。目前的工作将研究盐度的周期性变化对(i)渗透诱导的细胞大小变化的程度的影响；（ii）细胞溶质浓度的变化；（三）对这些变化的调节反应的细胞机制。实验将集中在双壳类鱼鳃对盐度胁迫的反应上，双壳类鱼鳃是一种特别适合使用直接光学和直接放射性示踪剂方法测量细胞体积的组织。这种技术的结合将允许在完整的动物和分离的组织中测量体积调节的程度。拟议研究的结果将导致对细胞体积调节对河口动物能量收支影响的首次评估。

9407997 Wright Because of the very large concentrations of salt in seawater, marine animals live under constant salinity stress. Marine invertebrates generally cope with this stress by maintaining in their cells a combination of inorganic solutes that together balance the large osmotic concentration of full strength sea water. Estaurine invertebrates face an added challenge. As a consequence of the daily change in tides, the estaurine environment can cyclically shift from full strength sea water to freshwater. Animals living in the intertidal habitats can, therefore, be exposed to changes in ambient osmolarity that can have a profound impact on their physiology. In particular, when exposed to reduced osmolarity (i.e., dilute sea water), the cells and tissues of estaurine animals typically swell. It is widely believed that the response of cells to this type of stress includes a loss of solute that induces an osmotically-obligated loss of water and hence a reduction in volume back toward normal levels. Indeed, this has been shown to be the case for many mammalian cells. For an estaurine animal faced with large daily shifts in osmolarity, any loss of solute must be met by an equal gain in solute when the tide shifts and ambient osmolarity returns to normal. Although these cyclic losses and gains of cell solute could represent a substantial energy cost to the animal, the actual extent of the energetic stress associated with exposure to cycles is unknown. The present work will examine the influence of cyclic changes in salinity on (i) the extent of osmostically-induced changes in cell size; (ii) the accompanying changes in cell solute concentration; and (iii) the cellular mechanism of the regulatory response to these changes. The experiments will focus on the response to salinity stress of bivalve gills, a tissue uniquely suited to measurement of cell volume using both direct optical and direct radiotracer methods. This combination of techniques will permit measu rement of the extent of volume regulation in intact animals as well as in isolated tissues. The results of the proposed studies will lead to the first assessment of the impact of cell volume regulation on the energy budget of an estaurine animal.