Ca²⁺ and Mg²⁺ transport in gills and gut of tilapia, Oreochromis mossambicus: A review

Abstract

The euryhaline tilapia Oreochromis mossambicus kept in fresh water takes up cal cium mainly from the water via the gills, like other freshwater fish. In the gills specialized mitochondria-rich cells, the chloride cells, are thought to mediate a transcellular Ca2+ transport. Second messenger operated calcium channels (SMOCs) in the apical membrane, regulated by the hormone stanniocalcin, allow minute-to-minute control over the entry of Ca2 +. In the basolateral plasma membranes of these cells, an ATP-consuming Ca2+ transporting enzyme provides the major driving force for extrusion of Ca2+ into the blood; in addition, an Na + /Ca2+ exchanger is present in these membranes. The kinetics of the exchanger in vitro indicate that this extrusion mechanism dominates when intracellular calcium levels reach micromolar levels. In the gills, the transport of calcium appears primarily ATPase mediated and therefore largely independent of the Na + status of the transporting cell. In enterocytes, similar mechanisms for transcellular transport of Ca2 + exist. However, in the intestinal epithelium the extrusion of Ca2 + is primarily via the Na + /Ca2 + exchanger and to a very limited extent mediated via the Ca2 +-ATPase. Indeed, calcium transport over the intestinal epithelium is dependent on the Na +-status and the N a+/K +-ATPase activity of the epi thelium. Prolactin and cortisol are endocrine factors determining the relative densities of calcium pumps in basolateral plasma membranes.At least 80% of the magnesium required for growth and homeostasis is absorbed from the food via the intestine. Magnesium is transported transcellularly and actively via enterocytes. The movement of Mg2 + over the apical membrane is passive, down an electrochemical gradient. The cytosolic Mg2 + concentration is kept well below its equilibrium concentration. The extrusion over the basolateral plasma membrane is mediated by an ATP-consuming enzyme. The gills contribute less than 20% to magnesium uptake, but up to 50% in tilapia fed a magnesium deficient diet. Evidence is accruing that prolactin is involved in the adaptation to low magnesium diets.

Diet influences salinity preference of an estuarine fish, the killifishFundulus heteroclitus

“…Dietary Ca 2+ appears to be taken up in substantial amounts in both freshwater (Bucking and Wood, 2007) and seawater fish (Bucking et al, 2011). Intestinal uptake of Ca 2+ is thought to be Na + dependent (Flik et al, 1993;Flik et al, 1990) and is likely to involve a Na + /Ca 2+ exchanger. The results of the current study suggest that Ca 2+ uptake from the diet is not influenced by changes in salinity (Table3, Fig.4) and probably does not explain the apparent inability to regulate plasma Ca…”

Localization of calbindin D28K-like immunoreactivity in fish gill: a light microscopic and immunoelectron histochemical study

“…The active uptake of calcium across the gills is probably concentrated in the chloride cells. Biochemical analysis of the gills of fish resulted in the demonstration of an ATP-dependent C a2" -transporting enzvme and a sodium gradient driven C a2 ' -exchanger in the basolateral cell membranes of these cells [28]. It is possible that the calbindin present at the surface of the epithelial lining is functionally related to the transport of calcium across the gill epi thelium.…”

Dietary Ca inhibits waterborne Cd uptake in Cd-exposed rainbow trout, Oncorhynchus mykiss

“…The rise in plasma calcium may induce mobilization of stanniocalcin, a calcitropic hormone known to regulate the activ-Ž ity of SMOCs via a second messenger reviewed . in Flik et al, 1993 . In turn, stanniocalcin release may inhibit calcium and cadmium influx through the SMOCs, thereby disrupting calcium homeostasis and leading eventually to hypocalcemia in plasma and reduced cadmium accumulation in body tissues.…”