Warm acclimation changes the expression of the Na super(+),K super(+)-ATPase alpha subunit isoforms in Antarctic fish gills

• Published in: Journal of experimental marine biology and ecology 2006-05, Vol.333 (1), p.129-139
• Main Authors: Morrison, John F, Guynn, Sierra R, Scofield, Margaret A, Dowd, Frank J, Petzel, David H
• Format: Article
• Language: English
• Subjects: Marine; Teleostei; Trematomus bernacchii
• ISSN: 0022-0981
• DOI: 10.1016/j.jembe.2005.12.048

Acclimation of the Antarctic teleost Trematomus bernacchii at + 4 degree C results in a 25% decrease in serum osmolality and a doubling of gill Na super(+),K super(+)-ATPase activity relative to - 1.5 degree C. Protein and mRNA of the alpha 1, alpha 2, and alpha 3 isoforms of Na super(+),K super(+)-ATPase were previously reported in T. bernacchii gill and studies in other systems have shown these isoforms display different kinetic and physiologic properties. We propose that the increase in Na super(+),K super(+)-ATPase activity resulting from + 4 degree C acclimation is due to a change in Na super(+),K super(+)-ATPase alpha isoform contribution and accounts for the decrease in serum osmolality. In response to acclimation at + 4 degree C, the apparent affinity of the enzyme for sodium increased significantly (measured by K super(') sub(Na) and K sub(0.5Na)), while the apparent affinity for potassium and ATP showed no change. Analysis of Na super(+),K super(+)-ATPase phosphoenzyme intermediates indicated the alpha 3 contribution to total Na super(+),K super(+)-ATPase decreased from 33.72 +/- 13.03% to 0 +/- 6.67% while alpha 1 and alpha 2 increased from 33.12 +/- 12.72% and 33.15 +/- 0.30% to 44.87 +/- 6.67% and 55.12 +/- 6.67%, respectively, upon + 4 degree C acclimation. Immunoblotting of alpha isoform protein showed significant increases in alpha 1 and alpha 2 and a significant decrease in alpha 3 with + 4 degree C acclimation. However, there was not a significant change in the Na super(+),K super(+)-ATPase alpha subunit steady state transcription levels as measured by real-time RT-PCR. These observations (through the application of a functional biochemical characterization to an environmental physiological change) suggest that the T. bernacchii reduce serum osmolality in response to increased environmental temperature by altering the alpha subunit composition of Na super(+),K super(+)-ATPase.