| Summary: | The Antarctic teleost Trematomus bernacchii lives in a saltwater environment with an average temperature of -1.8°C. These fish possess several unique adaptations including a serum osmolality that is nearly double that of temperate teleosts. Upon warm acclimation to +4°C, the T. bernacchii show a decrease in serum osmolality by nearly 25%, a doubling of gill Na+/K+-ATPase activity, and an increase in Na+/K+-ATPase expressing Cl cells. The Na+/K+- ATPase is also found in ion absorptive cells in the ceca, proximal and distal gut.|The serum osmolality of +1°C and +4°C acclimated fish were significantly lower after nine days than that of the control -1.5°C acclimated fish. While previously published data reported an increase in Na+/K+-ATPase activity upon warm acclimation to +4°C and an increase in Cl cells expressing the Na+/K+- ATPase enzyme, current data resulted in no significant change in Na+/K+- ATPase in either the +4°C or the +1°C acclimated groups. Immunostaining of the gill Cl cells also resulted in a significant decrease in cells staining positive for a1 isoform and the Na7K+/2CI' and no change in the Cl cells staining positive for the a3 isoform and the pan α antibody which recognizes all three isoforms of the Na+/K+-ATPase enzyme.|The pan α antibody stained positive in the ceca, proximal and distal intestinal regions at both -1.5°C and +4°C after four weeks of acclimation. The a3 isoform was also present under these conditions. However, the a1 isoform does not appear to be present in the three regions of the intestine. This is the first study we are aware of that indicates the absence of the a1 isoform of the Na+/K+-ATPase within the T. bernacchii ceca, proximal and distal alimentary tract. ProQuest Traditional Publishing Option xi, 103 pages
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