Caldesmon regulates the three-dimensional contraction (myosin-dependent contraction of the actin binding protein-induced actin gel).

We managed to develop a three-dimensional contractile model system using gizzard smooth muscle contractile elements. Phosphorylation of myosin was prerequisite for contraction. A high Mr actin-binding protein (ABP, or filamin), which cross-links actin filaments into a three-dimensional meshwork, was an essential factor for the three-dimensional contraction. Caldesmon suppressed contraction through the inhibition of the actin-ABP and actin-myosin interactions. Further, it was found that calmodulin could overcome the inhibitory effects of caldesmon on the above interactions, resulting in contraction. The possibility of this contractile model system being applied to nonmuscle contractile event is also discussed.