INHIBITORY EFFECTS OF MICROCYSTIS-AERUGINOSA TOXIN ON ION PUMPS OF THE GILL OF FRESH-WATER FISH

A microsomal fraction enriched in ion pump enzymes was isolated from the gill of the carp (Cyprinus carpio Linneo). Mg2+-dependent (Na+ + K+), Na+, HCO3- and Ca2+-stimulated ATPase activities were studied following treatment with microcystin-LR-like toxin, the major toxic component isolated from Microcystis aeruginosa culture. These enzyme activities were inhibited in a dose-dependent manner. The maximum inhibition of each enzyme, induced with nM concentration of the toxin, was similar to that produced by inhibitors specific for each ATPase activity. The Mg2+-ATPase activity and non-specific hydrolysis of ATP were unaffected. These results strongly suggest that the massive fish death during M. aeruginosa blooms may result from the loss of ion homeostatic processes produced by the inhibitory action of microcystin on the ion pumps of gill chloride cells.