| Cadmium?Cd?is one of the major metal pollutants in the aquatic ecosystem in Dongting Lake basin.It not only seriously affects the survival of fish,but also endangers human health through the food chain.Research shown:Calcium?Ca?and cadmium enrichment in fish tissues have significant antagonistic effects,with two mechanisms.One is that the radii of cadmium and calcium ions are similar.In the gill epithelial chlorine-secreting cells,Cd can inhibit the absorption of Ca by competing for high-affinity Ca binding sites with Ca.Another theory is that Cd inhibits Ca ions from entering into gill cells by competing for calcium pump and Ca2+-ATPase activity in the base of chlorine secreting cells,but the detailed mechanism remains to be further analyzed.For this reason,grass carp was used as the experimental object in this study,under the conditions of control group(0.003 mg/l Cd2++1.5 mg/l Ca2+),low calcium group(0.003 mg/l Cd2++2.5 mg/l Ca2+),medium calcium group(0.003 mg/l Cd2++3.0 mg/l Ca2+)and high calcium group(0.003mg/l Cd2++3.5 mg/l Ca2+),the physiological and biochemical characteristics of different tissues of grass carps and their gill transcriptome can further enrich and analyze the antagonistic mechanism of calcium and cadmium.The main research results are as follows:?1?Adding calcium in low concentration cadmium has no significant effect on grass carp growth and survival?p>0.05?.The order of cadmium enrichment in different tissues of grass carps in the experimental was:intestine>kidney>gill>liver,and calcium enrichment was highest in the gills.Calcium addition had a significant effect on cadmium enrichment in grass carps?p<0.05?.Cadmium concentration in gill,kidney,intestine and liver decreased with the increase of calcium concentration in water.The results showed that calcium could significantly inhibit cadmium enrichment in grass carps.?2?The concentration of Na+in grass carp plasma decreased with the increase of Ca concentration?p<0.05?.Muscle SOD activity,CAT activity and MDA content in the high calcium group were significantly higher than those in other groups.The high content of MDA influence the dynamic balance between the production and clearance of reactive oxygen species in muscles,while the increased activity of SOD and CAT indicates that the addition of calcium enhances the stress effect of grass carp on cadmium toxicity.The Ca2+-ATPase activity of grass carps gills in the experimental group was significantly higher than that in the control group.The results showed that the addition of Ca could improve the activity of Ca2+-ATPase,enhance the competitiveness of Ca against Cd,and thus reduce the damage of Cd to the gill epithelial cells.?3?There were 253 genes with the highest expression difference between the control group and the high-calcium group,among which 73 genes were up-regulated and 180 genes were down-regulated,while the genes with the lowest expression difference between the low-calcium group and the medium-calcium group were 34 genes with 15 up-regulated genes and 19 down-regulated genes.GO enrichment analysis showed that the most calcium-related differentially expressed genes were found in the control group and the high-calcium group?83 genes?,followed by the control group and the low-calcium group?44 genes?,while few genes were found in other groups.Differentially expressed genes mainly include calcium channel activity,calcium ion transmembrane transport,calcium ion chelation regulation,and cytoplasmic calcium ion concentration regulation.The results showed that the antagonistic effect of calcium on cadmium enrichment in grass carps might be related to the differential expression of calcium channel related genes in the gill. |
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