Water calcium concentration modifies whole-body calcium uptake in sea bream larvae during short-term adaptation to altered salinities

Abstract

Whole-body calcium uptake was studied in gilthead sea bream larvae (9-83·mg) in response to changing environmental salinity and [Ca 2+ ]. Calcium uptake increased with increased fish size and salinity. Fish exposed to calcium-enriched, diluted seawater showed increased calcium uptake compared with fish in diluted seawater alone. Calcium uptake was unchanged in Na + -enriched, diluted seawater. Overall, [Ca 2+ ], and not salinity/osmolarity per se, appears to be the main factor contributing to calcium uptake. By contrast, drinking was reduced by a decrease in salinity/osmolarity but was little affected by external [Ca 2+ ]. Calculations of the maximum contribution from drinking-associated calcium uptake showed that it became almost insignificant (less than 10%) through a strong decrease in drinking rate at low salinities (0-8‰). Diluted seawater enriched in calcium to the concentration present in full-strength seawater (i.e. constant calcium, decreasing salinity) restored intestinal calcium uptake to normal. Extra-intestinal calcium uptake also benefited from calcium addition but to a lesser extent.

The influence of environmental calcium concentrations on calcium flux, compensatory drinking and epithelial calcium channel expression in a freshwater cartilaginous fish

“…Once in the cell, Ca 2+ is bound to proteins and actively pumped across the basolateral membrane into the blood by Ca 2+ -specific ATPases or exchanged for Na + in Na + /Ca 2+ exchangers facilitated by the Na + gradient created by Na + ,K + -ATPase (Hwang and Lee, 2007). In the GIT, Ca 2+ uptake occurs following dietary ingestion (Bucking and Wood, 2007) and drinking (Flik et al, 1995;Guerreiro et al, 2004). Drinking may play a larger role in marine fishes, whereby the drinking of seawater offsets dehydrative water loss, and is also a potential source of Ca environments, GIT Ca 2+ uptake may be minimized through reduced transcellular transport and increased excretion via paracellular pathways (Schoenmakers et al, 1993), and luminal Ca 2+ obtained through drinking is largely precipitated by the bicarbonate base (Wilson et al, 2002).…”

Parathyroid hormone gene family in a cartilaginous fish, the elephant shark (Callorhinchus milii)

“…Pthrp's role in bony fish has been studied, (11,32,33) and it may be a hypercalcemic factor, particularly in the gills. (34) The role of Pthrp in elephant shark remains to be investigated.…”

“…(10) Attempts to elucidate the normal role of Pthrp in bony fish indicated that it is probably a hypercalcemic factor (11,12) that has potential paracrine actions in skin and muscle. (10) This reflects its roles in bony-jawed vertebrates and indicates that functions have been conserved from fish to mammals.…”

“…Sections were cut at 4 mm and placed on positively charged slides. Polyclonal antisera were raised against synthetic peptides of elephant shark Pth1(1-14), Pth2 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), and Pthrp (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) by Auspep (West Melbourne, Australia). Sections were stained using the Leica Bond-Max Autostainer (Leica Biosystems, Mount Waverley, Victoria, Australia).…”

Endocrine regulation of carbonate precipitate formation in marine fish intestine by Stanniocalcin and PTHrP

“…In addition to regulation of the amount of water ingested by endocrine and environmental factors (Fuentes et al, 1996;Fuentes and Eddy, 1997a;Fuentes and Eddy, 1997b;Guerreiro et al, 2004;Guerreiro et al, 2001), the processing of imbibed fluid has a major impact in fish ion regulation. Ingested water is first processed in the oesophagus, where it undergoes selective absorption of NaCl (Hirano and Mayer-Gostan, 1976;Parmelee and Renfro, 1983), which lowers fluid osmolality and is believed to enhance water absorption in the intestine.…”