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

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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.