Plasticity and stressor specificity of osmotic and heat shock responses of Gillichthys mirabilis gill cells

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Abstract
Short-term effects of osmotic and heat shock on proteins of Gillichthys mirabilis gill cells were analyzed. The protein synthesis rate (PSR) of gill cells was influenced by hyperosmotic shock (335-->635 mosmol/kgH2O) and heat shock (25-->37 degrees C), but not by hyposmotic shock (335-->190 mosmol/kgH2O). Between 4 and 6 h after hyperosmotic shock, gill cell protein synthesis was inhibited relative to controls in serum-free medium but increased threefold over control values in medium supplemented with 10% serum. Serum-dependent stimulation of PSR was also observed after heat shock. By use of two-dimensional electrophoresis, 21 proteins, induced after hyperosmotic shock, 14 after hyposmotic shock, and 16 after heat shock were found. The osmotic shock response of gill cells was highly stressor specific because only five or three proteins that were induced after hyperosmotic or hyposmotic shock, respectively, were identical to proteins induced in response to heat shock. Heat shock protein 70 isoforms were only induced after heat shock, but not in response to osmotic shock. In gill and kidney epithelium, the transcription factor c-Jun was modified within 30 min after transfer of whole fish from 1,086 mosmol/kgH2O to 5 or 2,172 mosmol/kgH2O, but osmotic shock in vitro had no effect on c-Jun in isolated gill cells. Ion-substitution experiments revealed that the increase of PSR after hyperosmotic shock in serum-supplemented medium significantly depended on an elevation of extracellular Na+ concentration. These data provide evidence for the plasticity and stressor specificity of osmotic and heat shock responses of fish gill cells.