Effect of cadmium on carbonic anhydrase and Na+-K+-ATPase in eel, Anguilla anguilla, intestine and gills

The effect of the heavy metal cadmium on in vitro activities of Na+-K+-ATPase and carbonic anhydrase (CA) in intestine and gills of the European eel, Anguilla anguilla, was analyzed. Na+-K+-ATPase enzymatic activities, measured in intestinal and branchial homogenates, were inhibited by increasing cadmium concentrations (0.5-50 mu M, after 1 h of incubation) in a dose-dependent manner; the maximal inhibition (about 80%) was observed at 5 mu M and 50 mu M CdCl2 for the branchial and intestinal Na+-K+-ATPase respectively. Carbonic anhydrase activities, measured in gill homogenate and in cytosolic and brush border membrane fractions isolated from intestinal mucosa, were significantly inhibited by pre-incubation (1 h) with CdCl2. Maximal inhibition (about 80%) of branchial CA was noted at approximately 60 mu M; higher concentrations evoked no further significant inhibition. Intestinal CA isoforms, cytosolic and membrane-bound, exhibited lower sensitivity to the heavy metal with respect to the branchial CA activity, since the highest concentration of CdCl2 tested (600 mu M) produced an inhibition of about 30% and 50% respectively. The results of the present study suggest that cadmium, by inhibiting the activity of CA and Na+-K+-ATPase enzymes in intestine and gills, could alter both acid-base balance and osmoregulation in teleostean fish. (C) 1998 Elsevier Science Inc. All rights reserved.