ISSN:
1432-136X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. Branchial activities of Na+−K+-ATPase, ouabain-insensitive ATPase, (Mg++-ATPase) and Ca++-ATPase were measured inGillichthys mirabilis after adaptation to salinities ranging from 170% SW to FW. Stabilities of these activities against freezing and deoxycholate solubilization and the temperature-dependence of activity rates were also investigated. Subcellular distribution and some kinetic properties of these activities, and of SDH were compared in branchial tissues of fish adapted to 170% SW and to FW. 2. Na+−K+-ATPase was maximally active at a Na+ concentration of 180 mM and K+ concentration of 60 mM. This enzyme was least active in 100% SW-adapted animals, but showed elevated activity after adaptation to 170% SW and to FW.Gillichthys is unusual (but not unique) among euryhaline teleosts by displaying higher Na+−K+-ATPase in FW- than in SW-adapted animals. Greatest activity, however, was observed in the heavy microsomal fraction (34,000xg) of the 170% SW-adapted group. Maximum SDH activity was also observed in the mitochondrial fraction (25,000xg) of 170% SW-adapted fish. 3. Activity of Ca++-ATPase displayed a complex Ca++-dependence. Two kinetic forms of this activity could be resolved, one with a high Ca++-affinity (K m=2.9 μM), the other having low Ca++-affinity (K m=0.88 mM). The low-affinity activity was reduced in branchial homogenates of 170% SW-compared with FW-adapted fish; the heavy microsomal fraction (34,000xg) derived from gills was most enriched in this Ca++-dependent ATPase in FW-adaptedGillichthys. In contrast, activities of the high-affinity form were equally enriched in heavy microsomal fractions of 170% SW- and FW-adapted animals. The high-affinity Ca++-ATPase was far more sensitive to inhibition by deoxycholate treatment than the low-affinity component. The possible roles of heterogeneous Ca++-dependent activities in branchial Ca++-transport are discussed. 4. Gill Mg++-ATPase activity was significantly elevated in FW and in 5% SW-adapted animals compared with the marine (170% SW- and 100% SW-adapted fish). The Mg++-dependent activity was most concentrated in the heavy microsomal fraction and to a lesser extent in the light microsomal and mitochondrial fractions in both 170% SW- and FW-adaptedGillichthys.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00782593
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