The Role of Polyamines in Osmotic Stress Tolerance in Gulf Killifish Fundulus grandis

Abstract

Polyamines are a family of low molecular weight organic cations produced in part by the coordinated actions of arginase II (Arg II) and ornithine decarboxylase (Odc). Although little is known of their functions in fish, polyamines have been implicated in diverse physiological processes. We describe a possible role of polyamines in hypoosmotic tolerance in the gulf killifish, Fundulus grandis, a species known to tolerate acute fluctuations in wide salinity range. Adult fish were reared in 5 ppt water for at least 1 month, and acutely transferred to 0.1, 0.5, 1, 2, and 5 ppt. Fish were randomly sampled from each salinity at 6 h, 1 d, 3 d, and 7 d post‐transfer. We have shown that relative Arg II and Odc mRNA levels, and Odc protein activity are highly up‐regulated in the gills. Hypoosmotic exposure also increases the concentration of the polyamines, putrescene, spermidine, and spermine. Although gill putrescine levels remain elevated throughout the first 7 days post ‐ transfer to freshwater, the concentrations of spermidine and spermine decrease with time suggesting a catabolic regulation of compounds. We are investigating the role of polyamine catabolism in apoptosis during salinity‐induced gill remodeling.