Inhibition by trifluoperazine and digitonin of several forms of pinocytosis

The effect of the calmodulin antagonist trifluoperazine on fluid phase, adsorptive and receptor-mediated pinocytosis in cultured human fibroblasts and mouse peritoneal macrophages was studied. Uptake in each case was reversibly inhibited by about 20% without toxic effects. Low concentrations of the detergent digitonin had a similar effect. Thus the three uptake mechanisms have common features, and we suggest that in both fibroblasts and macrophages they may reflect uptake within vesicles participating in receptor-mediated endocytosis. These effects of trifluoperazine may operate directly on membranes without the participation of calmodulin.