Okadaic acid. Protein phosphatase inhibition and muscle contractile effects.

Okadaic acid (OA;C44H66O13) is a polyether derivative of a C38 fatty acid first isolated from marine sponges of the genus Halichondria . 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. Physiologically, OA has been known to have a marked contractile effect on smooth muscles and heart muscle. Recent results strongly suggest that these contractile effects are due to the inhibitory action of OA on the intracellular protein phosphatase activity.