Cl−Uptake Mechanism in Freshwater‐Adapted Tilapia (Oreochromis mossambicus)

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Abstract
In this study, the correlation between Cl(-) influx in freshwater tilapia and various transporters or enzymes, the Cl(-)/HCO(3)(-) exchanger, Na(+),K(+)-ATPase, V-type H(+)-ATPase, and carbonic anhydrase were examined. The inhibitors 2x10(-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 6x10(-4) M DIDS (a Cl(-)/HCO(3)(-) exchanger inhibitor) caused 40%, 60%-80%, 40%-60%, and 40%-60% reduction in Cl(-) influx of freshwater tilapia, respectively. The inhibitor 2x10(-4) 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(-)/HCO(3)(-) exchanger, and carbonic anhydrase may be involved in the active Cl(-) uptake mechanism in gills of freshwater-adapted tilapia.