Hsp70 and a 54 kDa protein (Osp54) are induced in salmon (Salmo salar) in response to hyperosmotic stress

Hsp70 and a 54 kDa osmotic stress protein (osp54) were induced in isolated tissues of anadromous Atlantic salmon (Salmo salar) upon exposure to hypero smotic conditions. Incubation of branchial lamellae, hepatic tissue, and er ythrocytes in medium supplemented with 200-600 mM NaCl dramatically reduced protein synthesis. Although general protein synthesis remained depressed f ollowing transfer of tissues from 450 mM supplemental NaCl to iso-osmotic m edium, hsp70 was prominently induced in branchial lamellae and hepatic tiss ue. Accumulation of hsp70 mRNA and a decrease in actin mRNA suggest prefere ntial upregulation of the hsp70 gene. Induction of osp54 was observed in br anchial lamellae and erythrocytes, but not in hepatic tissue, during exposu re to 75-125 mM supplemental NaCl. Use of glycerol in place of NaCl to crea te hyperosmotic conditions stimulated induction of hsp70 in branchial lamel lae. Substitution with mannitol resulted in induction of osp54 in both bran chial lamellae and erythrocytes. The solute-specific and temporal patterns of response suggest that hsp70 and osp54 might function in concert to resto re osmotic homeostasis and renature proteins destabilized or denatured duri ng the early stages of osmotic shock. (C) 1999 Wiley-Liss, Inc.