Cl- uptake mechanism in freshwater-adapted tilapia (Oreochromis mossambicus)

In this study, the correlation between Cl- influx in freshwater tilapia and various transporters or enzymes, the Cl-/HCO3- exchanger, Na+, K+-ATPase, V-type H+-ATPase, and carbonic anhydrase were examined. The inhibitors 2 x 10(-4) M ouabain (a Na+, K+-ATPase inhibitor), 10(-5) M NEM ( a V-type H+-ATPase inhibitor), 10(-2) M ACTZ (acetazolamide, a carbonic anhydrase inhibitor), and 6 x 10(-4) M dIDS (a Cl-/HCO3- exchanger inhibitor) caused 40%, 60% - 80%, 40% - 60%, and 40% - 60% reduction in Cl- influx of freshwater tilapia, respectively. The inhibitor M ouabain also caused 50% - 65% inhibition in gill Na+, K+-ATPase activity. Western blot results showed that protein levels of gill Na+, K+-ATPase, V-type H+-ATPase, and carbonic anhydrase in tilapia acclimated in low-Cl- freshwater were significantly higher than those acclimated to high-Cl- freshwater. Based on these data, we conclude that Na+, K+-ATPase, V- H+-ATPase, the Cl-/ HCO3- exchanger, and carbonic anhydrase may be involved in the active Cl- uptake mechanism in gills of freshwater-adapted tilapia.