Effect of citreoviridin, a mycotoxin from Penicillium citreoviride, on kinetic constants of acetylcholinesterase and ATPase in synaptosomes and microsomes from rat brain

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The subcutaneous injection of acute (6 mg/kg) and subacute doses of citreoviridin, a toxin from Penicillium citreoviride NRRL 2579, inhibited brain synaptosomal (Na + + K +)-ATPase whereas in microsomes, both (Na + + K +)-ATPase and Mg 2+-ATPase activities are significantly stimulated in a dose-dependent manner. In vitro, both Mg 2+ and (Na + + K +)-ATPase activities are inhibited in synaptosomal as well as in microsomal fractions. Kinetic parameters obtained from double reciprocal plots indicate that under in vivo conditions citreoviridin increases V max and K m values of microsomal (Na + + K +)-ATPase and Mg 2+-ATPase, whereas in synaptosomes Mg 2+-ATPase, V max and K m are unaltered but (Na + + K +)-ATPase V max is decreased and K m increased. In vitro, both Mg 2+ and (Na + + K +)-ATPase K m values are increased and V max values are decreased in the synaptosomal as well as in the microsomal fractions. On the other hand, AChE V max values are decreased and K m values are increased in the synaptosomes under both in vivo and in vitro conditions. In microsomes, in vivo, the V max values are decreased and K m values are unaltered while in vitro both are unaltered. These results indicate that citreoviridin neurotoxicity may be related to the altered enzymatic activities.