Influence of Dietary Sodium on Waterborne Copper Toxicity in Rainbow Trout, Oncorhynchus Mykiss

Abstract

Juvenile rainbow trout were fed diets containing control (0.26 mmol/g) or elevated (1.3 mmol/g) dietary Na+ in combination with either background (19 nmol/L) or moderately elevated levels (55 or 118 nmol/L) of waterborne Cu for 21 d. Unidirectional waterborne Na+ uptake rates (measured with 22Na) were up to four orders of magnitude higher than those of Cu (measured with 64Cu). Chronic exposure to elevated dietary Na+ alone or in combination with elevated waterborne Cu decreased whole-body uptake rates of waterborne Na+ and Cu. Accumulation of new Cu and Na+ at the gills was positively and highly significantly correlated and responded to the experimental treatments in a similar fashion, suggesting that Na+ and Cu have common branchial uptake pathways and that dietary Na+ preexposure modifies these pathways. Chronic exposure to elevated waterborne Cu significantly increased Cu concentrations in the liver but caused only modest increases in total Cu concentrations in the whole body and gill. Chronic exposure to elevated dietary Na+ slightly decreased whole-body Cu concentration on day 14 and greatly reduced liver Cu concentration on days 14 and 21; new Cu accumulation in whole-body, gill, and internal organs was reduced on all days. Chronic exposure to elevated waterborne Cu or dietary Na+ alone reduced short-term gill Cu binding at low waterborne Cu concentrations. At high waterborne Cu concentrations, chronic exposure to elevated waterborne Cu had no effect, while elevated dietary Na+ increased Cu binding to the gills. Combined chronic exposure to elevated dietary Na+ and waterborne Cu decreased gill Cu binding over the entire range of Cu concentrations tested. Clearly, chronic exposure to elevated dietary Na+ and waterborne Cu appears to modify gill Cu-binding characteristics and may be important considerations in future development of a chronic biotic ligand model for Cu.

Interaction of dietary sodium chloride and waterborne copper in rainbow trout (Oncorhynchus mykiss): copper toxicity and sodium and chloride homeostasis

“…Specifically, exposure of freshwater fish to elevated dietary NaCl suppresses branchial Na + uptake (Smith et al 1995;Kamunde et al 2003;, increases diffusive Na + efflux via the gills (Smith et al 1995;Pyle et al 2003), and increases renal Na + excretion (Salman and Eddy 1987). Our data are consistent with these findings.…”

“…Consequently, sampling after a substantial period of starvation (e.g., Kamunde et al 2003) is unlikely to capture these apparently transient changes in tissue Na + levels.…”

“…Several recent studies have advanced the concept that freshwater fish can take advantage of dietary ion surplus to mitigate the toxicity of waterborne toxicants that inhibit branchial ion uptake Pyle et al 2003;Baldisserotto et al 2004). Specifically, Kamunde et al (2003) and Pyle et al (2003) demonstrated that elevated dietary Na + reduced gill binding and unidirectional uptake of waterborne Cu in rainbow trout while simultaneously decreasing branchial Na + uptake. Although the reduction in uptake and gill binding of Cu essentially implies reduction in Cu toxicity, protection against waterborne Cu toxicity by dietary NaCl is yet to be unambiguously demonstrated.…”

Sodium-sensitive and -insensitive copper accumulation by isolated intestinal cells of rainbow troutOncorhynchus mykiss

“…These indirect effects would raise whole cell Cu content as Na + o declines, giving the impression of apparent Na + o -dependent Cu uptake. In vivo, there may also be systemic Na + -dependent modulation of Cu uptake (systemic Na + effects on Cu uptake by trout gills; Kamunde et al, 2003;Pyle et al, 2003).…”

Uptake, handling, and excretion of Na+ and Cl- from the diet in vivo in freshwater and seawater-acclimated killifish, Fundulus heteroclitus, an agastric teleost

“…The explanation for the marginal effect in freshwater killifish may be a matter of threshold. In critically reviewing a number of saltfeeding papers on salmonids (Smith et al, 1995;Kamunde et al, 2003;Pyle et al, 2003;Niyogi et al, 2006), Wood and Bucking (Wood and Bucking, 2011) concluded that the threshold for increases in branchial Na + efflux rate lay above a salt concentration of 1270μmolNa It would be interesting to test whether the same considerations apply to uptake and retention of Cl -from high-and low-salt diets in the freshwater killifish. However, cost considerations precluded repeating the experiment with low-salt diets labelled with 36 Cl -.…”