Abstract
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 Ca2+ uptake in the context of Ca2+ 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 Ca2+ uptake in zebrafish. Transepithelial Ca2+ transport in NaRC, through apical epithelial Ca2+ channels (ECaC), basolateral plasma membrane Ca2+-ATPase (PMCA), and Na+/Ca2+ exchanger (NCX), is analogous to mammalian renal and intestinal Ca2+-absorption cells. Several hormones were demonstrated to differentially regulate Ca2+ uptake through modulating the expression of Ca2+ 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 Ca2+ 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 Ca2+ 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.
Highlights
Ca2+ is required for diverse intracellular and extracellular physiological activities, such as neurotransmission, muscle contraction, and bone remodeling [1,2]; and vertebrates have to maintain Ca2+ homeostasis in body fluids
Liao et al revealed that atp1a1a.1 expression in zebrafish was stimulated by acclimation to a low Ca2+ water, suggesting that atp1a1a.1 provides the Na+ gradient to drive the operation of NCX1b [11]
Previous studies indicated the mRNA expression of epithelial Ca2+ channels (ECaC) in zebrafish embryos was differently regulated by external Ca2+ levels [8,18,19,21,33,34]
Summary
Ca2+ is required for diverse intracellular and extracellular physiological activities, such as neurotransmission, muscle contraction, and bone remodeling [1,2]; and vertebrates have to maintain Ca2+ homeostasis in body fluids. Zebrafish has been an emerging animal model to explore the regulatory mechanism of ionic homeostasis in body fluid in recent years [15,16,17]. Liao et al revealed that atp1a1a.1 expression in zebrafish was stimulated by acclimation to a low Ca2+ water, suggesting that atp1a1a.1 provides the Na+ gradient to drive the operation of NCX1b [11] Taking these results together, the model of transepithelial Ca2+ transport in zebrafish NaRC is similar to that in the kidneys and intestine of mammals. Previous studies indicated the mRNA expression of ECaC in zebrafish embryos was differently regulated by external Ca2+ levels [8,18,19,21,33,34]. We will introduce the role of calcium-sensing receptor (CaSR) in the regulation of calciotropic hormones, and the mutual interplay of those hormones in terms of body fluid Ca2+ homeostasis in zebrafish
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