Calcium homeostasis in crustaceans: subcellular Ca dynamics.

The molting cycle of crustaceans, associated with renewal and remineralization of the cuticle, has emerged as a model system to study regulation of genes that code for Ca(2+)-transporting proteins, common to all eukaryotic cells. This article reviews state-of-the-art knowledge about how crustacean transporting epithelia (gills, hepatopancreas and antennal gland) effect mass transcellular movement of Ca(2+) while preventing cytotoxicity. The current model proposed is based on in vitro research on the intermolt stage with extrapolation to other molting stages. Plasma membrane proteins involved in apical and basolateral Ca(2+) movement (NCX, PMCA) are contrasted between aquatic species of different osmotic origin and among transporting epithelia of an individual species. Their roles are assessed in the context of epithelial Ca(2+) flux derived from organismic approaches. Exchange with extracellular environments is integrated with Ca(2+) sequestration mechanisms across endomembranes of the ER/SR and mitochondria. Finally, the review postulates how new Ca(2+) imaging techniques will allow spatial and temporal resolution of Ca(2+) concentration in subcellular domains.