PLASTICITY AND STRESSOR SPECIFICITY OF OSMOTIC AND HEAT-SHOCK RESPONSES OF GILLICHTHYS MIRABILIS GILL CELLS

Short-term effects of osmotic and heat shock on proteins of Gillichthy s mirabilis gill cells were analyzed. The protein synthesis rate (PSR) of gill cells was influenced by hyperosmotic shock (335 --> 635 mosmo l/kgH(2)O) and heat shock (25 --> 37 degrees C), but not by hyposmotic shock (335 --> 190 mosmol/kgH(2)O). Between 4 and 6 h after hyperosmo tic shock, gill cell protein synthesis was inhibited relative to contr ols in serum-free medium but increased threefold over control values i n medium supplemented with 10% serum. Serum-dependent stimulation of P SR was also observed after heat shock. By use of two-dimensional elect rophoresis, 21 proteins induced after hyperosmotic shock, 14 after hyp osmotic shock, and 16 after heat shock were found. The osmotic shock r esponse of gill cells was highly stressor specific because only five o r three proteins that were induced after hyperosmotic or hyposmotic sh ock, respectively, were identical to proteins induced in response to h eat shock. Heat shock protein 70 isoforms were only induced after heat shock, but not in response to osmotic shock. In gill and kidney epith elium, the transcription factor c-Jun was modified within 30 min after transfer of whole fish from 1,086 mosmol/kgH(2)O to 5 or 2,172 mosmol /kgH(2)O, but osmotic shock in vitro had no effect on c-Jun in isolate d gill cells. Ion-substitution experiments revealed that the increase of PSR after hyperosmotic shock in serum-supplemented medium significa ntly depended on an elevation of extracellular Na+ concentration. Thes e data provide evidence for the plasticity and stressor specificity of osmotic and heat shock responses of fish gill cells.