Abstract
Okadaic acid (OA; C44H66O13) is a polyether derivative of a C38 fatty acid first isolated from marine sponges of the genusHalichondria (Tachibanaet al. 1981). It is thought to be synthesized by marine diflagellates and to accumulate in the other marine organisms such as sponges and shellfishes which feed on them (Yasumotoet al. 1985). Physiologically, OA has been known to have a marked contractile effect on smooth muscles (Shibataet al. 1982) and heart muscle (Kodamaet al. 1986). Recent results strongly suggest that these contractile effects are due to the inhibitory action of OA on the intracellular protein phosphatase activity (Takaiet al. 1987; Bialojanet al. 1988; Hescheleret al. 1988; Bialojan & Takai, 1988).