Subcellular distribution of Cd and Zn and MT mRNA expression in the hepatopancreas of Sinopotamon henanense after single and co-exposure to Cd and Zn

The freshwater crab Sinopotamon henanense was exposed to Cd and Zn either on their own or in combination. At 14 and 28 days the hepatopancreas was taken and total metal and metallothionein MT) in transcript abundance were assessed. In addition, the subcellular contents of Cd and Zn also were examined following a differential centrifugation. The results showed that concentration of Cd was more responsive to waterborne metal exposures than the concentration of Zn; Zn was better regulated and exhibited only 2-3 fold increases relative to the control. Of the subcellular fractions, the heat stable protein (HSP) fraction was the predominant metal-binding compartment for Cd. The proportion and accumulation of Cd in this fraction increased with the single Cd exposures, which suggest that metallothionein-like proteins play a key role in metal detoxification in the hepatopancreas of S. henanense. Despite the increases in Cd in the HSP fraction during single Cd exposures, some accumulation of Cd was observed in metal sensitive fraction (MSF), which showed that metal detoxification was incomplete. The results demonstrated that the Cd content decreased in metal mixture groups especially when mixed with higher Zn, while the Cd accumulation in MSF was also reduced when Zn was added. MT mRNA expression was also determined in our report, the results showed that both Cd and Zn had the ability of inducing MT mRNA expression. Additionally, the MT mRNA transcription level was enhanced when Cd was mixed with Zn.