Effects of extracts from the cyanobacterium Microcystis aeruginosa on ion regulation and gill Na+,K+-ATPase and K+-dependent phosphatase activities of the estuarine crab Chasmagnathus granulata (Decapoda, Grapsidae)

Recent discoveries indicate that microcystins affect enzymes, such as Na+, K+-ATPase, involved in ion regulation of aquatic animals, through K+-dependent phosphatase inhibition. In vitro studies showed the inhibitory effect of Microcystis aeruginosa extracts on Na+, K+-ATPase and K+-dependent phosphatase activities in gills of Chasmagnathus granulata (Decapoda, Grapsidae). Extracts of M. aeruginosa were prepared from lyophilized or cultures cells of the cyanobacterium. For lyophilized cells, IC50 values were estimated as 0.46 mug/L (95% confidence interval [CI]=0.40-0.52 mug/L) and 1.31 mug/L (95% CI=1.14-1.51 mug/L) for Na+, K+-ATPase and K+-dependent phosphatase, respectively. However, extracts prepared from cultured cells presented a much lower inhibitory potency against both enzymes. Gas chromatography revealed long-chain fatty acids in the lyophilized cell extracts, indicating that they are in part responsible for the enzyme inhibition. In vivo studies showed that the toxin inhibited Na+, K+-ATPase activity in anterior gills, whereas an increased augmented activity of glutathione-S-transferase was observed in both kind of gills, indicating that the crab has increased its ability to conjugate the toxin. No significant differences in hemolymph sodium or chloride concentration were detected. This result is in agreement with the lack of effects of microcystin on Na+, K+-ATPase activity of posterior (osmoregulating) gills.