Okadaic acid, a polyether fatty acid associated with diarrhetic seafood poisoning, is capable of inhibiting protein phosphatases 1 and 2A which are considered among the major protein phosphatases in the cytosol of mammalian cells. One of the substrates for these phosphatases has been reported to be the cytoskeleton. In this paper, we focused on the effects of okadaic acid in intestinal cells, the more physiological target for this toxin. By fluorescence and scanning electron microscopy, we evidenced a dose- and time-dependent effect on F-actin which preceded any detectable change of tubulin and vimentin network. By a flow cytometric approach, we observed that plasma membrane permeability and transmembrane potential, two indicators of early cell damage or activation, respectively, remained unaffected in intoxicated cells. The present data strongly support the theory that actin is one of the main cytosolic targets for the phosphatases inhibited by okadaic acid in intestinal cells.
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