CRUSTACEAN MODELS FOR STUDYING CALCIUM-TRANSPORT - THE JOURNEY FROM WHOLE ORGANISMS TO MOLECULAR MECHANISMS

The crustacean moult cycle is a convenient model system in which to st udy calcium (Ca) homeostasis as vectorial movement across Ca transport ing epithelia (gills, gastric epithelium, cuticular hypodermis, antenn al gland) which occurs in either direction at different stages of the moulting cycle. Intermoult crustaceans are in relative Ca balance. Dur ing premoult, at the same time as the cuticle decalcifies, epithelia i nvolved in Ca storage (e.g. gastric) calcify and/or increase their int racellular Ca stores. Premoult Ca balance is typically negative as Ca is excreted. During postmoult the soft new cuticle is remineralized la rgely with external Ca taken up across the gills and gastric epitheliu m (positive Ca balance); conversely during this time internally stored Ca is remobilized. This review (1) compares the relative roles of Ca transporting epithelia in Ca balance for crustaceans from different ha bitats; (2) proposes up-to-date cellular models for both apical to bas olateral and basolateral to apical Ca transport in both noncalcifying and calcifying epithelia; (3) compares kinetics of the Ca pump and exc hanger during intermoult; (4) presents new data on specific activity o f calcium adenosinetriphosphatase (Ca(2+)ATPase) during the moult cycl e of crayfish and (5) characterizes a partial cDNA sequence for the cr ayfish sarcoplasmic reticular Ca(2+)ATPase and documents its expressio n in gill, kidney and muscle of intermoult crayfish. The physiological and molecular characterization of Ca transporters in crustaceans will provide insight into the function, regulation and molecular evolution of mechanisms common to all eukaryotic cells.