OXIDATION OF NITRITE TO NITRATE IN ISOLATED ERYTHROCYTES - A POSSIBLEMECHANISM FOR ADAPTATION TO ENVIRONMENTAL NITRITE

Rainbow trout (Oncorhynchus mykiss) were exposed to nitrite (0.007 mmo l NO2-. L-1) for 48 days. During the first 14 days, the methaemoglobin concentration in the blood as well as the NO2- and NO3- concentration s in the plasma increased whereas further days of exposure led to a de crease in the nitrite, nitrate, and methaemoglobin concentrations in t he blood. Isolated erythrocytes from rainbow trout have the ability to detoxify nitrite by oxidation to nitrate, thus removing this compound from the blood. This process is dependent on oxygen loading of haemog lobin and on the nitrite concentration in the medium. In anoxic erythr ocytes the oxidation of nitrite to nitrate is drastically reduced. Ass uming Michaelis-Menten kinetics, the uptake for nitrite in our investi gation was estimated between 1.06 and 2.21 mu mol NO2-. h(-1). kg fish (-1). After 14 days of exposure approximately 20% of the total NO2- ta ken up will be detoxified by erythrocytes in fish. We hypothesize that rainbow trout have the capacity for adapting to nitrite exposure by i ncreasing the rate of oxidation to nitrate.