BIOCHEMICAL-CHARACTERIZATION OF MICROCYSTIN TOXICITY IN RAINBOW-TROUT(ONCORHYNCHUS-MYKISS)

The kinetics and biochemical effects of microcystins in rainbow trout were studied with freeze-dried toxic cells of Microcystis aeruginosa, strain PCC 7806. Following in vivo exposure the changes in liver histo logy were observed over a 72 hr period and the absorption of microcyst ins from the gastrointestinal tract into the blood and liver, as well as the inhibition of hepatic protein phosphatase 1 and 2A activities, were recorded using the protein phosphatase inhibition assay. The inte raction between microcystins and trout liver phosphatases was further tested in vitro using the protein phosphatase inhibition assay. The in vivo experiments demonstrated a high organotropy of microcystins for the liver, where rapid and total inhibition of protein phosphatase 1 a nd 2A activity was observed. Maximal inhibition of phosphatases was ob served 3 hr after gavage. At that time-point, approximately 63% of the toxin present in the liver was refractive to detection via the phosph atase inhibition assay and therefore most likely covalently bound to c ellular proteins. The inhibition of hepatic protein phosphatases 1 and 2A proved to be transient only, as a progressive increase in phosphat ase activity was observed beginning 12 hr after gavage of the fish, re aching approximately 50% of the control activity at 72 hr. In contrast , liver damage continued to progress despite this renewed protein phos phatase activity. (C) 1997 Elsevier Science Ltd.