Heat pretreatment increases cadmium resistance and HSP 70 levels in BalticSea mussels

The effects of heat treatment and cadmium exposure on the synthesis of a ma jor stress inducible protein (hsp 70) and on the metabolism of the blue mus sel Mytilus edulis L. from the:Baltic Sea, were studied in a laboratory exp eriment. The mussels were kept in sea water of ambient salinity (6.3 parts per thousand) and temperature (4 degrees C). The effects of cadmium (20 mu g l(-1)), measured as changes in physiological rates (oxygen consumption, a mmonia excretion, clearance rates and scope for growth) and hsp 70 expressi on were studied at 4 degrees C and in combination with a rapid rise in temp erature to 20 degrees C. Relatively low levels of hsp 70 were detected but the negative effect was reflected in a reduction of scope for growth of the exposed mussels compared to controls. This effect was more pronounced at 2 0 degrees C. Mussels not exposed to cadmium in the first experiment were us ed in a second set of experiments. Heat shocked mussels were allowed to rea cclimatise to 4 degrees C for 5 days and then, along with the mussels alrea dy at 4 degrees C, exposed to cadmium (20 mu g l(-1)). The:results clearly indicated that the mussels exposed to 20 degrees C in the first experiment more rapidly induced synthesis of hsp 70 after cadmium exposure in the seco nd experiment. Also the reacclimatised mussels exposed to heat shock but no t to cadmium in the first experiment, induced some hsp 70 in the second exp eriment. This suggests that the rate of induction of heat shock or stress p roteins in Baltic mussels is slower than what has been described for mussel s from more marine environments. The mussels kept at 4 degrees C throughout the experiment and exposed to cadmium showed low levels of hsp 70, again i ndicating a low rate of induction. The increasing levels of hsp 70 correlat ed well with a maintained level of physiological fitness, in terms of scope for growth, although the mussels showed increasing body burdens of cadmium . (C) 2000 Elsevier Science B.V. All rights reserved.