Regulation of motility in nonmuscle cells.

In the past several years actomyosin contractile systems have been related to many types of cell movement and other functions such as cytoplasmic streaming, cytokinesis, blood clot retraction, and phagocytosis. The evidence for the presence of actin and myosin in nonmuscle cells is now widespread and has been the subject of a recent review (85) and two recent published symposia Regulation of these processes is complicated and probably involves more than one mechanism. In vivo and in vitro studies have shown that calcium may regulate some of these motile systems in a way similar to calcium regulation in muscle: MgATP (adenosine 5'-triphosphate) and micromolar concentrations of free calcium ion are required for functional actin-myosin interaction (contraction) to take place. This may be a target for some of the intracellular calcium. The purpose of this review is to evaluate recent advances in our understanding of the regulation of these cellular motile processes. The evidence for calcium control of motility in vivo and in cellular models will be presented. This will be followed by a discussion of the types of regulation that have been found or might be expected on the basis of existing studies of muscle and nonmuscle cells. Emphasis will be placed on work that has been published since the 1974 Pollard and Weihing review (85).