High waterborne Mg does not attenuate the toxic effects of Fe, Mn, and Ba on Na+ regulation of Amazonian armored catfish tamoata (Hoplosternum litoralle)

摘要

Formation water (FoW) is a by-product from oil and gas production and usually has high concentrations of soluble salts and metals. Calcium (Ca) and magnesium (Mg) have been shown to reduce the toxicity of metals to aquatic animals, and previous study showed that high waterborne Ca exerts mild effect against disturbances on Na+ regulation in Amazonian armored catfish tamoata (Hoplosternum littorale) acutely exposed to high Fe, Mn, and Ba levels. Here, we hypothesized that high Mg levels might also reduce the toxic effects of these metals on Na+ regulation of tamoata. The exposure to 5% FoW promoted an increase in Na+ uptake and a rapid accumulation of Na+ in all tissues analyzed (kidney plasma gills carcass liver), besides increasing the branchial activity of both NKA and v-type H+-ATPase in fish. High waterborne Mg lowered Na+ efflux rates and markedly inhibited Na+ uptake, and also reduced both NKA activity and newly Na+ accumulation in gills of fish. High Fe levels increased Na+ net losses and inhibited Na+ uptake in tamoata. The diffusive Na+ losses and the newly accumulated Na+ in gills were reduced in fish exposed to high Mn and Ba. High waterborne Ba also inhibited NKA in gills, while both high Mn and Ba inhibited v-type H+-ATPase in kidney of tamoata. High Mg did not lessen the toxic effect of Fe on Na+ net fluxes, and reduced even more Na+ uptake and the newly Na+ accumulation in gills and plasma, and did not prevent the inhibition of both NKA and v-type H+-ATPases in kidney. Furthermore, Mg did not attenuate the effect of Mn on inhibition Na+ uptake, keeping the activity of v-type H+-ATPase in kidney significantly lowered. High Mg levels mildly attenuated the effects of Ba in Na+ balance by increasing the new accumulation of Na+ in liver, and restore the activity of both NKA and v-type H+-ATPase in gills of tamoata. Overall, high waterborne Mg does not have a strong contribution to, or have only minor effects, in protecting tamoata against disruptions in Na+ regulation mediated by high Fe, Mn, and Ba levels.