Different expression patterns of heat shock proteins hsp 60 and hsp 70 in zebra mussels (Dreissena polymorpha) exposed to copper and tributyltin

To investigate the dose-response relationship of the expression of heat shock proteins hsp 60 and hsp 70 following exposure to environmentally-relevant contaminants, zebra mussels (Dreissena polymorpha) were exposed to sublethal concentrations of copper and tributyltin (TBT). Mussels were exposed to Cu (0-500 mu g/l) or TBT (0-75 mu g/l) for 24 h. Hsp 60 and hsp 70 expression relative to the controls was analyzed by western blotting and densitometry. Contaminant concentrations in the exposure medium and mussel tissues were measured by atomic absorption spectroscopy (AAS) or high resolution gas chromatography with flame photometric detection (HRGC-FPD) for Cu and TBT, respectively. Following copper exposure, hsp 60 showed a biphasic expression pattern, with a maximal expression of three times control levels at 22 mu g Cu/g dry wt., while hsp 70 concentrations reached a plateau of approximately 2.5 times control levels after crossing an induction threshold at tissue concentrations of less than 29 mu g Cu/g dry wt. In contrast, concentrations of both hsp 60 find hsp 70 were increased to approximately 2.5-3 times control levels in TBT-exposed mussels at all tested doses. The results of this study demonstrate that the nature of the dose-response curves depend on both the form of stress protein investigated (hsp 60 or hsp 70) and on the contaminant. The implications for the use of hsp 60 and hsp 70 as biomarkers in ecotoxicological research are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.