Caldesmon is a developmentally regulated protein involved in smooth muscle and non-muscle contraction. Two closely related variants of human caldesmon have been identified which differ in their eletrophoretic mobility and cellular distribution. The h-caldesmon variant (120-150kDa) is predominantly expressed in smooth muscle whereas l-caldesmon (70-80kDa) is found in non-muscle tissue and cells. Neither of the two variants has been detected in skeletal muscle.