Effect of phalloidin and viroisin on Acanthamoeba castellanii after permeabilization of the cell.

We have developed a new technique for the permeabilization of the membrane of Acanthamoeba castellanii. This technique involves the use of digitonin which alters neither the morphology nor the motility of the cell, but favours the penetration of phalloidin and viroisin. Treatment of permeabilized cells with phalloidin or viroisin induces, in the cortex of the cell, an intensive proliferation of filaments which have been identified as actin. This cortical filamentous layer detaches from the membrane and slowly contracts, acting as a fine mesh sieve which concentrates the organelles in the middle of the cell, causing therefore the formation of a central granuloplasm and a cortical hyaloplasm. During this process, cell motility is irreversibly lost. The results indicate that extensive proliferation and reorganization of actin filaments cannot support cell motility and they are discussed in terms of a general understanding of amoeboid movement.