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

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 Mg²⁺-ATPase activities are significantly stimulated in a dose-dependent manner. In vitro, both Mg²⁺ 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 Mg²⁺-ATPase, whereas in synaptosomes Mg²⁺-ATPase, V_max and K_m are unaltered but (Na⁺ + K⁺)-ATPase V_max is decreased and K_m increased. In vitro, both Mg²⁺ 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.