Characterization of transport Na+-ATPases in gills of freshwater tilapia |
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| Authors: | Dr Paul Balm Nico Goossen Sjef van de Rijke Sjoerd Wendelaar Bonga |
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| Institution: | (1) Department of Animal Physiology, Faculty of Science, University of Nijmegen, Toernooiveld 25, 6525 ED Nijmegen, The Netherlands |
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| Abstract: | Branchial plasma membranes from the freshwater cichlid teleostOreochromis mossambicus (tilapia) contain two Na+-dependent ATPases: Na+/K+ ATPase, and an amiloride-sensitive ATPase which is postulated to operate as a Na+/H+ (–NH4
+) ATPase. It is suggested that both enzyme activities are located in the basolateral membrane system of the chloride cells. K+ has opposing effects on the two enzymes: it stimulates Na+/K+ ATPase and inhibits Na+/H+ (–NH4
+) ATPase activity. Na+/H+ ATPase appears more sensitive to NH4
+ at low concentrations than Na+/K+ ATPase and the stimulatory effect by NH4
+ ions on the first enzyme could be important in facilitating NH4
+ excretion by tilapia gills under physiological conditions.In vitro maximum stimulation by NH4
+ is similar for the two enzymes (200%). In contrast to Na+/K+ ATPase, Na+/H+ ATPase activity is inhibited by supra-physiological (>20 mM) concentrations of NH4
+. |
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| Keywords: | sodium transport Na+/K+ ATPase Na+/H+ (– NH4
+) ATPase tilapia gills |
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