Physiological Mechanisms of Calcium Regulation Using the Molting Cycle of a Freshwater Crayfish as a Model System

钙在生物体中起着重要的生理作用。它是生物矿物的主要成分。细胞外水平参与兴奋分泌偶联，而细胞内水平最近被认为是协调细胞反应的信使。本研究拟以淡水小龙虾的蜕皮周期作为研究钙离子调控机制的模型系统。甲壳动物是这方面的理想选择，因为它们交替进行钙离子吸收(骨骼沉积)和钙离子输出(骨骼吸收)。相关的机制在淡水(离子受限)物种中是高度精细的。这项研究将在7个实验水平上完成：(1)整个动物的钙离子(及其相关电解质--Na+、Cl-、HCO3-、H+)和水在身体组织中的分布；(2)鳃的通量；(3)肾滤过后加工；(4)细胞外调节的电化学基础；(5)骨骼和软组织调节；(6)模拟表皮下层的上皮运输；(7)钙、钠/钾-三磷酸腺苷转运酶和碳酸氢酶的亚细胞分布。这些参数中的每一个都将在21℃的人工自来水中进行自然蜕皮(对照)的小龙虾进行研究。该项目的完成将极大地促进我们对上皮细胞钙双向运输的机制和控制的总体理解，特别是参考甲壳类蜕皮。

Calcium plays important physiological roles in living organisms. It is a major component of biominerals. Extracellular levels are involved in excitation secretion coupling and intracellular levels have recently been implicated as messengers in coordinating cellular responses. This proposal intends to use the molting cycle of the freshwater crayfish as a model system in which to study mechanisms of Ca2+ regulation. Crustaceans are ideal for this since they alternately undergo Ca2+ uptake (skeletal deposition) and Ca2+ output (skeletal resorption). The associated mechanisms are highly refined in freshwater (ion limited) species. The study will be completed at 7 experimental levels which are (1) whole animal Ca2+ (and associated electrolyte--Na+, Cl-, HCO-3, H+) and water distribution among body tissues; (2) branchial fluxes; (3) renal postfiltrational processing; (4) the electrochemical basis of extracellular regulation; (5) skeletal and soft tissue regulation; (6) epithelial transport modeled on an isolated cuticular hypodermis and (7) subcellular distribution of transport enzymes Ca2+ and Na+/K+ ATPases and carbonic anhydrase. Each of these parameters will be studied in crayfish undergoing natural molts in artificial tap water (controls) at 21 C. Completion of the project should significantly advance our general understanding of the mechanisms and control of bidirectional epithelial Ca2+ transport with specific reference to crustacean molting.