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摘要
The main objective of this study was to understand the mode of interaction between waterborne copper (Cu) and high environmental ammonia (HEA) exposure on freshwater fish, and how they influence the toxicity of each other when present together. For this purpose, individual and combined effects of Cu and HEA were examined on selected physiological and ion-regulatory processes and changes at transcript level in the common carp (Cyprinus carpio). Juvenile carp were exposed to 2.6 mu M Cu (25% of the 96 h LC50 value) and to 0.65 mM ammonia (25% of the 96 h LC50 value) singly and as a mixture for 12 h, 24 h, 48 h, 84 h and 180 h. Responses such as ammonia (J(amm)) and (J(urea)) (I excretion rate, plasma ammonia and urea, plasma ions (Na+, Cl- and K+), muscle water content (MWC) as well as branchial Na+/K+-ATPase (NKA) and H+-ATPase activity, and branchial mRNA expression of NKA, H+-ATPase, Na+/H+ exchanger (NHE-3) and Rhesus (Rh) glycoproteins were investigated under experimental conditions. Results show that J(amm) was inhibited during Cu exposure, while HEA exposed fish were able to increase excretion efficiently. In the combined exposure, J(amm) remained at the control levels indicating that Cu and HEA abolished each other's effect. Expression of Rhcg (Rhcg-a and Rhcg-b) mRNA was upregulated during HEA, thereby facilitated ammonia efflux out of gills. On the contrary, Rhcg-a transcript level declined following Cu exposure which might account for Cu induced J. inhibition. Likewise, Rhcg-a was also down-regulated in Cu-HEA co-exposed fish whilst a temporary increment was noted for Rhch-b. Fish exposed to HEA displayed pronounced up-regulation in NKA expression and activity and stable plasma ion levels. In both the Cu exposure alone and combined Cu-HEA exposure, ion-osmo homeostasis was adversely affected, exemplified by the significant reduction in plasma [Na+] and [Cl-], and elevated plasma [K+], along with an elevation in MWC. These changes were accompanied by a decline in MCA activity. Gill H+-ATPase mRNA levels and activities were not affected by either Cu or HEA or both. Likewise, NHE-3 expression remained unaltered but tended to be numerically higher during HEA exposure. Overall, these data suggest that at equitoxic concentrations (25% of 96 h LC50), the individual effect of Cu is more harmful while HEA induces quicker adaptive responses. Our findings also denote a competitive mode of interaction, exemplified by the inhibition of HEA-mediated adaptive responses in the presence of Cu.
- 出版日期2016-1
