EFFECTS OF CHROMIUM(VI) ON SOME ION-DEPENDENT ATPASES IN GILLS, KIDNEY AND INTESTINE OF A COASTAL TELEOST PERIOPHTHALMUS DIPES

The coastal teleost species, Periophthalmus dipes, commonly known as t he mudskipper, was exposed to three sublethal concentrations (5, 10 an d 15 mg/l) of potassium chromate for three exposure durations (2, 4 an d 6 days). The study compares the dose- and duration-dependent effects of Cr(VI), as potassium chromate, on the ATPase systems in various or gans of this fish species. In this study, effects of Cr(VI) stress on total ATPase, (Na+,K+)-ATPase, (Ca++)-ATPase, (Mg++)-ATPase, (Ca++,HCO 3-)-ATPase and (Mg++,HCO3-)-ATPase in gills, kidney and intestine were estimated. A general dose- and duration-dependent inhibitory trend wa s observed. However, it is evident that exposure duration is more impo rtant then dose in the inhibition of the activity of the enzymes. At s ome concentrations, initial stimulation of the activity of some enzyme s were also noticed. However, maximum inhibition was observed in highe r Cr(VI) concentrations exposed for the longest time. It is possible t hat this inhibition of the ATPases by Cr(VI) blocked the active transp ort system of the gill epithelial as well as chloride cells, glomerula r and epithelial cells of the tubules and thus altered the osmoregulat ory mechanism of the fish. It appears that this heavy metal ion alters the membrane permeability of the intestinal epithelial cells and othe r layer of cells by altering the activity of ATPases, resulting in a b reakdown of the active transport mechanism needed for the absorption o f nutrients, ions and metabolites.