Calcium uptake in the skin of a freshwater teleost.

Abstract

The skin, particularly the opercular membrane of some teleosts, contains mitochondrion-rich "chloride" cells and has been widely used as a model to study branchial salt-extrusion mechanisms in seawater fish. Skin isolated from the operculum of the freshwater Nile tilapia (Oreochromis nilotcus) can transport Ca2' against an ionic and electrical gradient. Adaptation of Nile tilapia to a low-Ca21 environment increased the capacity ofthe opercular membrane to transport Ca2+. The density of mitochondrion-rich cells increased in parallel with Ca2' transport capacity. The results demonstrate net Ca2+ uptake by vertebrate skin and strongly implicate mitochondrion-rich cells as the site of Ca2+ uptake in fresh water.Calcium is necessary for a variety of functions in animals, including bone and scale growth, muscle contraction, transmission of nerve impulses, hormone secretion, and intracellular signaling. In animals living in fresh water, calcium can be obtained from food or from the surrounding medium. Freshwater fish have the capacity to maintain normal blood Ca2+ levels (2-4 mM) in a wide range of external Ca2+ concentrations (<0.01 mM), even when food is withheld for long periods (1-3). Although the gills (4-12) and skin (5, 13) have both been implicated as sites of Ca2`uptake in teleosts, net Ca2' uptake in isolated skin or gill tissue has not, to our knowledge, previously been demonstrated. The present study was undertaken to determine whether net Ca2' uptake occurs in fish skin in vitro and whether mitochondrion-rich (MR) cells are involved in Ca2+ uptake. MATERIALS AND METHODSThe Nile tilapia Oreochromis niloticus is an Old World cichlid endemic to the freshwater lakes of the Rift Valley of Africa. Juvenile Nile tilapia, weighing 40-60 g and previously reared in fresh water, were kept in 33-liter tanks maintained at 24 + 1°C with charcoal filtration and aeration. Fish were kept in either freshwater (FW: 0.77-1.04 mM Na+/0.54-0.58 mM Ca2+) or low-Ca2+ freshwater (LCFW: deionized water supplemented with NaCl, 0.50-0.97 mM Na+, and 0.003-0.011 mM Ca2+). Fish were maintained under experimental conditions for at least 2 weeks before sampling and were fed a maintenance ration of commercial trout chow (0.5% body weight per day). Water samples were taken intermittently from tanks containing fish to determine environmental [Na+] and [Ca2W]. Although LCFW solution contains normal, freshwater concentrations of Na+ and Cl-, it has low levels of other ions; we explicitly assume that the results obtained are due to decreased Ca2+; absence of other divalent ions does not cause morphological changes in teleost gills (14). Environmental and total plasma [Na+] and [Ca2+] were measured by atomic absorption spectrophotometry. Two-thirds of the tank volume in each group was replaced every other day. Food was withheld for 24 hr before sampling of individual fish. Fish were killed by cranial concussion and pithing and were bled from the caudal vessels into heparinized syringes. Plasma was isolated by centrifugation and sto...

Calcium balance in sea bream (Sparus aurata): the effect of oestradiol-17beta

“…opercular membrane; McCormick et al 1992, Marshall et al 1992 and from the diet via the intestine. In the present study, we aimed to determine the contribution of the intestine to calcium regulation since marine fish drink large amounts of seawater (containing 10 mmol/l calcium in our experiments) and the intestine is known to play an important role in osmoregulation.…”

“…The majority of the calcium transport mechanisms are proposed to take place actively at the level of the gills (Flik et al 1995) and, at least in some species, partly through the skin (McCormick et al 1992, Marshall et al 1992. In fresh water, fish drink very little and as a consequence virtually all the calcium incorporated via the intestine is of dietary origin.…”

The Presence of High-Affinity, Low-Capacity Estradiol-17β Binding in Rainbow Trout Scale Indicates a Possible Endocrine Route for the Regulation of Scale Resorption

“…The gills are considered to account for a large part of the calcium uptake by freshwater fish (Mashiko and Jozuka, 1962;Perry and Wood, 1985;Flik et al, 1985a), and active calcium uptake mechanisms have been demonstrated in the gills of several teleost species (Flik et al, 1984(Flik et al, , 1985bFlik and Perry, 1989). Further, some environmental calcium uptake can occur across skin and fins (Mashiko and Joshuka, 1962;Perry and Wood, 1985), and it has been shown that teleost skin is capable of active calcium uptake, with the calcium transporting capacity increasing with the density of mitochondriarich cells (Marshall et al, 1992;McCormick et al, 1992).…”

Calcium deficiency-induced and TRP channel-regulated IGF1R-PI3K-Akt signaling regulates abnormal epithelial cell proliferation

“…As in the case of human colonic epithelium, a reduction in water Ca 2 þ concentration ([Ca 2 þ ]) increases NaR cell number on the yolk sac skin in zebrafish embryos and larvae. 11 In fact, acclimation to low [Ca 2 þ ] has been shown to increase ionocyte number and/or density in the adult gills in many teleost species for more than two decades, 12,13 suggesting an evolutionarily conserved regulatory mechanism at work.…”