The Control of Calcium Metabolism in Zebrafish (Danio rerio).

Zebrafish is an emerging model for the research of body fluid ionic homeostasis. In this review, we focus on current progress on the regulation of Ca(2+) uptake in the context of Ca(2+) sensing and hormonal regulation in zebrafish. Na⁺-K⁺-ATPase-rich cells (NaRCs), the specialized ionocytes in the embryonic skin and adult gills, play a dominant role in Ca(2+) uptake in zebrafish. Transepithelial Ca(2+) transport in NaRC, through apical epithelial Ca(2+) channels (ECaC), basolateral plasma membrane Ca(2+)-ATPase (PMCA), and Na⁺/Ca(2+) exchanger (NCX), is analogous to mammalian renal and intestinal Ca(2+)-absorption cells. Several hormones were demonstrated to differentially regulate Ca(2+) uptake through modulating the expression of Ca(2+) transporters and/or the proliferation/differentiation of NaRC in zebrafish. In addition, the counterbalance among these hormones is associated with the maintenance of body fluid Ca(2+) homeostasis. Calcium-sensing receptor (CaSR) is expressed in several hormone-secreting tissues in zebrafish, and activated CaSR differentially controls calciotropic hormones. The major principles of Ca(2+) transport and the hormonal control appear to be conserved from zebrafish to other vertebrates including mammals. The new knowledge gained from zebrafish studies provides new insights into the related issues in vertebrates.