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James S. Ballantyne - One of the best experts on this subject based on the ideXlab platform.
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Intermediary metabolism of Arctic Char Salvelinus alpinus during short-term salinity exposure.
Journal of Experimental Biology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, James S. BallantyneAbstract:The migration of Arctic Char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic Char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated Char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic Char to seawater.
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Wild Arctic Char (Salvelinus alpinus) upregulate gill Na+,K+-ATPase during freshwater migration.
Physiological and biochemical zoology : PBZ, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
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wild Arctic Char salvelinus alpinus upregulate gill na k atpase during freshwater migration
Physiological and Biochemical Zoology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
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Membrane lipids of red muscle mitochondria from land-locked and sea-run Arctic Char, Salvelinus alpinus
Marine Biology, 1997Co-Authors: H. C. Glémet, M. F. Gerrits, James S. BallantyneAbstract:Although laboratory studies of the effects of temperature, salinity, and diet on biological membranes of fish indicate substantial alterations in phospholipid and fatty acid composition to maintain functional properties, there are few parallel studies of wild populations. We, therefore, examined the red muscle, mitochondrial phospholipids and phospholipid fatty acids in two fish populations differing in their environmental temperature, salinity, and diet. Sea-run and freshwater (land-locked) Arctic Char (Salvelinus alpinus L.) were collected from Igloolik Island, Northwest Territories, Canada, in the summer of 1991. Several differences between the phospholipids of these fish, and those reported for red muscle mitochondria in other fish species, included a higher cardiolipin content and a higher proportion of short-chain monoenes, especially 16:1. In congruence with previous studies of changes in cardiolipin fatty acids in other species of cold-acclimated fish, the fatty acid content of cardiolipin of both Arctic Char groups was more saturated and less polyunsaturated than in warm-acclimated fish. Other aspects of the lipid composition of these membranes were not consistent with laboratory studies of cold-acclimated fish. For example, the fatty acids comprising phosphatidylethanolamine and phosphatidylcholine were more saturated than would be predicted based on laboratory studies of cold-acclimated fish. Some of these differences may be attributable to differences in the proportions of dietary n3 and n6 fatty acids in freshwater and marine environments. A strategy common to both groups of Arctic Char is the maintenance of a similar relationship between phospholipid fatty acid chain length and degree of unsaturation in both Arctic Char populations in spite of differences in diet and thermal regimes. The observed differences in membrane composition between land-locked and sea-run fish presumably act to maintain mitochondrial function in these different environments.
Jason S. Bystriansky - One of the best experts on this subject based on the ideXlab platform.
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failure to up regulate gill na k atpase α subunit isoform α1b may limit seawater tolerance of land locked Arctic Char salvelinus alpinus
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, J S BallantyneAbstract:Many populations of Arctic Char (Salvelinus alpinus) are land-locked, physically separated from the ocean by natural barriers and unable to migrate to sea like anadromous populations. Previous studies which experimentally transferred land-locked Arctic Char to seawater report high mortality rates due to osmoregulatory failure and an inability to up-regulate gill Na(+),K(+)-ATPase activity. This study examined the mRNA expression of two recently discovered alpha-subunit isoforms of gill Na(+)K(+)-ATPase (alpha1a and alpha1b) during seawater exposure of land-locked Arctic Char. mRNA levels of these gill Na(+),K(+)-ATPasealpha-subunit isoforms were compared to Na(+),K(+)-ATPase activity and protein levels and related to osmoregulatory performance. Land-locked Arctic Char were unable to regulate plasma osmolality following seawater exposure. Seawater exposure did not induce an increase in gill Na(+),K(+)-ATPase activity or protein levels. Na(+),K(+)-ATPase isoform alpha1a mRNA quickly decreased upon exposure to seawater, while isoform alpha1b levels were unchanged. These results suggest the inability of land-locked Arctic Char to acclimate to seawater is due a failure to up-regulate gill Na(+),K(+)-ATPase activity which may be due to their inability to increase Na(+),K(+)-ATPase alpha1b mRNA expression.
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Intermediary metabolism of Arctic Char Salvelinus alpinus during short-term salinity exposure.
Journal of Experimental Biology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, James S. BallantyneAbstract:The migration of Arctic Char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic Char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated Char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic Char to seawater.
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Wild Arctic Char (Salvelinus alpinus) upregulate gill Na+,K+-ATPase during freshwater migration.
Physiological and biochemical zoology : PBZ, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
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wild Arctic Char salvelinus alpinus upregulate gill na k atpase during freshwater migration
Physiological and Biochemical Zoology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
Natasha Therese Frick - One of the best experts on this subject based on the ideXlab platform.
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failure to up regulate gill na k atpase α subunit isoform α1b may limit seawater tolerance of land locked Arctic Char salvelinus alpinus
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, J S BallantyneAbstract:Many populations of Arctic Char (Salvelinus alpinus) are land-locked, physically separated from the ocean by natural barriers and unable to migrate to sea like anadromous populations. Previous studies which experimentally transferred land-locked Arctic Char to seawater report high mortality rates due to osmoregulatory failure and an inability to up-regulate gill Na(+),K(+)-ATPase activity. This study examined the mRNA expression of two recently discovered alpha-subunit isoforms of gill Na(+)K(+)-ATPase (alpha1a and alpha1b) during seawater exposure of land-locked Arctic Char. mRNA levels of these gill Na(+),K(+)-ATPasealpha-subunit isoforms were compared to Na(+),K(+)-ATPase activity and protein levels and related to osmoregulatory performance. Land-locked Arctic Char were unable to regulate plasma osmolality following seawater exposure. Seawater exposure did not induce an increase in gill Na(+),K(+)-ATPase activity or protein levels. Na(+),K(+)-ATPase isoform alpha1a mRNA quickly decreased upon exposure to seawater, while isoform alpha1b levels were unchanged. These results suggest the inability of land-locked Arctic Char to acclimate to seawater is due a failure to up-regulate gill Na(+),K(+)-ATPase activity which may be due to their inability to increase Na(+),K(+)-ATPase alpha1b mRNA expression.
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Intermediary metabolism of Arctic Char Salvelinus alpinus during short-term salinity exposure.
Journal of Experimental Biology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, James S. BallantyneAbstract:The migration of Arctic Char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic Char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated Char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic Char to seawater.
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Wild Arctic Char (Salvelinus alpinus) upregulate gill Na+,K+-ATPase during freshwater migration.
Physiological and biochemical zoology : PBZ, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
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wild Arctic Char salvelinus alpinus upregulate gill na k atpase during freshwater migration
Physiological and Biochemical Zoology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
Eric B. Taylor - One of the best experts on this subject based on the ideXlab platform.
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Trophic biology and migratory patterns of sympatric Dolly Varden (Salvelinus malma) and Arctic Char (Salvelinus alpinus)
Canadian Journal of Zoology, 2016Co-Authors: Allison Dennert, Shannan L. May-mcnally, Morgan H. Bond, Thomas P. Quinn, Eric B. TaylorAbstract:The trophic ecology (diet and head morphology) and migration patterns of two closely related salmonid fishes, Arctic Char (Salvelinus alpinus (L., 1758)) and Dolly Varden (Salvelinus malma (Walbaum, 1792)), were examined in tributaries of Lake Aleknagik, southwestern Alaska, to test for differentiation between species. Schoener’s index of proportional overlap and multivariate analyses of diets suggested that these species had significantly different trophic niches. Arctic Char and the largest individuals of both species had the most diverse diets, and sockeye salmon (Oncorhynchus nerka (Walbaum, 1792)) eggs dominated the diet of both species, especially Arctic Char. Arctic Char had larger jaws and wider heads than Dolly Varden of similar body length, which may contribute to interspecific diet difference. The species also differed in migration patterns; otolith microchemistry indicated that juvenile Arctic Char were produced by nonanadromous mothers, whereas the mothers of the Dolly Varden had been to sea ...
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The Arctic Char (Salvelinus alpinus) "complex" in North America revisited.
Hydrobiologia, 2015Co-Authors: Eric B. TaylorAbstract:The Arctic Char (Salvelinus alpinus) species “complex” has fascinated biologists for decades particularly with respect to how many species there are and their geographic distributions. I review recent research on the species complex, focussing on biodiversity within northwestern North America, which indicates (i) what was once considered a single taxon consists of three taxa: S. alpinus (Arctic Char), S. malma (Dolly Varden), and S. confluentus (bull trout), (ii) morphological and genetic data indicate that S. alpinus and S. malma, and S. malma and S. confluentus exist as distinct biological species in sympatry, (iii) sympatric forms of S. alpinus exist in Alaska as in other areas of the HolArctic, (iv) Dolly Varden comprises two well-differentiated subspecies, S. m. malma and S. m. lordi, in the eastern Pacific and the northwestern Canadian Arctic that meet at a contact zone on the southern edge of the Alaska Peninsula, and (v) Dolly Varden and bull trout consist of several population assemblages that have legal status as distinct conservation units under US and Canadian law. This research has significantly revised what constitutes the S. alpinus species “complex”, provided insights into the ecology and genetics of co-existence, and promoted conservation assessment that better represents biodiversity within Salvelinus. A geographically and genetically comprehensive analysis of relationships among putative taxa of Pan-Pacific Salvelinus is still required to better quantify the number of taxa and their origins.
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evidence for genetic distinction among sympatric ecotypes of Arctic Char salvelinus alpinus in south western alaskan lakes
Ecology of Freshwater Fish, 2015Co-Authors: Shannan L Maymcnally, Thomas P. Quinn, Pamela J Woods, Eric B. TaylorAbstract:Resource polymorphism may play an important role in the process of speciation. The Arctic Char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic Char from five isolated yet proximate postglacial lakes in south-western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of Char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’-, ‘medium’-, and ‘small’-bodied Char; maximum FST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = −0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic Char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in HolArctic populations of Arctic Char.
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Evidence for genetic distinction among sympatric ecotypes of Arctic Char (Salvelinus alpinus) in south‐western Alaskan lakes
Ecology of Freshwater Fish, 2014Co-Authors: Shannan L. May-mcnally, Thomas P. Quinn, Pamela J Woods, Eric B. TaylorAbstract:Resource polymorphism may play an important role in the process of speciation. The Arctic Char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic Char from five isolated yet proximate postglacial lakes in south-western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P
J. G. Richards - One of the best experts on this subject based on the ideXlab platform.
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failure to up regulate gill na k atpase α subunit isoform α1b may limit seawater tolerance of land locked Arctic Char salvelinus alpinus
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, J S BallantyneAbstract:Many populations of Arctic Char (Salvelinus alpinus) are land-locked, physically separated from the ocean by natural barriers and unable to migrate to sea like anadromous populations. Previous studies which experimentally transferred land-locked Arctic Char to seawater report high mortality rates due to osmoregulatory failure and an inability to up-regulate gill Na(+),K(+)-ATPase activity. This study examined the mRNA expression of two recently discovered alpha-subunit isoforms of gill Na(+)K(+)-ATPase (alpha1a and alpha1b) during seawater exposure of land-locked Arctic Char. mRNA levels of these gill Na(+),K(+)-ATPasealpha-subunit isoforms were compared to Na(+),K(+)-ATPase activity and protein levels and related to osmoregulatory performance. Land-locked Arctic Char were unable to regulate plasma osmolality following seawater exposure. Seawater exposure did not induce an increase in gill Na(+),K(+)-ATPase activity or protein levels. Na(+),K(+)-ATPase isoform alpha1a mRNA quickly decreased upon exposure to seawater, while isoform alpha1b levels were unchanged. These results suggest the inability of land-locked Arctic Char to acclimate to seawater is due a failure to up-regulate gill Na(+),K(+)-ATPase activity which may be due to their inability to increase Na(+),K(+)-ATPase alpha1b mRNA expression.
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Wild Arctic Char (Salvelinus alpinus) upregulate gill Na+,K+-ATPase during freshwater migration.
Physiological and biochemical zoology : PBZ, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...
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wild Arctic Char salvelinus alpinus upregulate gill na k atpase during freshwater migration
Physiological and Biochemical Zoology, 2007Co-Authors: Jason S. Bystriansky, Natasha Therese Frick, J. G. Richards, Patricia M. Schulte, James S. BallantyneAbstract:Abstract The successful acclimation of eurhyhaline fishes from seawater to freshwater requires the gills to stop actively secreting ions and start actively absorbing ions. Gill Na+,K+‐ATPase is known to be an integral part of the active ion secretion model of marine fishes, but its importance in the active ion uptake model of freshwater fishes is less clear. This study, conducted in the high Arctic, examines gill Na+,K+‐ATPase regulation in wild anadromous Arctic Char returning to freshwater from the ocean. Gill Na+,K+‐ATPase activity, protein expression, and mRNA expression of Na+,K+‐ATPase isoforms α1a and α1b were monitored in Arctic Char at three points along their migration route to and from Somerset Island, Nunavut, Canada: out at sea (Whaler’s Point), in seawater near the river mouth (Nat’s Camp), and after entering the Union River. Arctic Char collected from the Union River had more than twofold greater gill Na+,K+‐ATPase activity. This was associated with a significant increase (threefold) in Na+...