The marine toxin okadaic acid is a potent neurotoxin for cultured cerebellar neurons.

The tumor promoter okadaic acid (OKA), is a marine toxin of algal origin, identified as a potent inhibitor of protein phosphatases 1 and 2A, and possibly enhancing calcium influx through voltage dependent calcium channels (VSSC). We now report that OKA at concentrations as low as 0.5 nM produced neurotoxicity, characterized first by the desintegration of the neurites and swelling of cell bodies, and later by cellular death. Non-neuronal cells viability and morphology were unaffected up to at least 5 nM OKA. Neurons sensitivity to the toxin changed with age in culture. Maximum neurotoxicity was observed in neurons at 9 DIC, when the OKA concentration producing half of the maximum reduction in neuronal survival (EC50) was approximately 0.65 nM. At 5 DIC or 19 DIC (EC50 approximately 2.5 nM and approximately 4.5 nM respectively), neurons appeared to be less sensitive to OKA. Neurotoxicity by OKA was not reduced by VSCC antagonists such as nifedipine and verapamil, nor by antagonists of excitatory aminoacid (EAA) receptors including APV, MK801 or CNQX. VSCC antagonists and EAA receptors antagonists fully protected from neurotoxicity induced by depolarization with KCl. These results suggest that OKA mechanism of neurotoxicity may not directly involve VSCC, endogenous EAA release and EAA receptors, but may depend upon other neurochemical events.