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 the mudskipper, was exposed to three sublethal concentrations (5, 10 and 15 mg/l) of potassium chromate for three exposure durations (2, 4 and 6 days). The study compares the dose- and duration-dependent effects of Cr(VI), as potassium chromate, on the ATPase systems in various organs of this fish species. In this study, effects of Cr(VI) stress on total ATPase, (Na+,K+)-ATPase, (Ca+2)-ATPase, (Mg+2)-ATPase, (Ca+2, HCO3-)-ATPase and (Mg+2,HCO3-)-ATPase in gills, kidney and intestine were estimated. A general dose- and duration-dependent inhibitory trend was observed. However, it is evident that exposure duration is more important then dose in the inhibition of the activity of the enzymes. At some concentrations, initial stimulation of the activity of some enzymes were also noticed. However, maximum inhibition was observed in higher Cr(VI) concentrations exposed for the longest time. It is possible that this inhibition of the ATPases by Cr(VI) blocked the active transport system of the gill epithelial as well as chloride cells, glomerular and epithelial cells of the tubules and thus altered the osmoregulatory mechanism of the fish. It appears that this heavy metal ion alters the membrane permeability of the intestinal epithelial cells and other layer of cells by altering the activity of ATPases, resulting in a breakdown of the active transport mechanism needed for the absorption of nutrients, ions and metabolites.