Adverse effects of sublethal concentration of cadmium on both protein expression profiles and on regulatory volume decrease.

It is known that cadmium is a very toxic metal released from various natural and anthropogenic sources. Since the aquatic environment is the ultimate sink of pollutants, the study of their effects on the resident organisms is of crucial importance. In the present work the effects of cadmium at cellular level were investigated on the digestive gland of Mytilus galloprovincialis, a well known bioindicator organism, by evaluating the Protein Expression Profiles (PEPs) and the RVD (Regulatory Volume Decrease) response in the gland of both control and treated animals (exposed to 40μgL-1 CdCl2 for 21 days). PEPs were obtained in the cytosolic fraction of digestive glands using two-dimension electrophoresis. Protein spots were detected with the PD-Quest analysis software. CdCl2 induced significant alterations: 47 new proteins were expressed, 143 suppressed, 30 proteins two-fold up-regulated, while 41 proteins two-fold down-regulated. The ability of the isolated cells of the digestive gland to regulate cell volume when exposed to an hypotonic medium was investigated by the aid of a videometric method. The cells of the treated animals, unlike those of the control ones, were not able to perform RVD. The observation that the cells of the control animals did not exhibit RVD when preincubated in the presence of 10-5 M cytocalasin D, know inhibitor of actin polymerization, and of 10-3 M ouabain, known inhibitor of the pump, suggests the importance of the integrity of cytoskeleton and of the activity of the Na+/K+/ATPase for the RVD response. These results led us to hypothesize that the inhibitory effect of RVD produced by Cd2+ could be due to its effect on the cytoskeleton and/or the pump, known targets of the metal, but other mechanisms cannot be excluded. The identification of the differently expressed proteins, showed by the proteomic analysis, could shed light on the cause of the impaired RVD in the presence of cadmium. Our results confirm the validity of the proteomic analysis and suggest the possibility to investigate the ability of the cell to cope an osmotic stress to detect the molecular effect of sublethal concentration of Cd in a bioindicator organism.