PH-DEPENDENT PERMEABILIZATION OF THE PLASMA-MEMBRANE OF MAMMALIAN-CELLS BY ANTHRAX PROTECTIVE ANTIGEN

Protective antigen (PA) of anthrax toxin forms ion-conductive channels in planar lipid bilayers and liposomes under acidic pH conditions. We show here that PA has a similar permeabilizing action on the plasma m embranes of CHO-K1 and three other mammalian cell lines (J774A.1, RAW2 64.7 and Vero). Changes in membrane permeability were evaluated by mea suring the efflux of the K+ analogue, Rb-86+, from prelabelled cells, and the influx of Na-22+. The permeabilizing activity of PA was limite d to a proteolytically activated form (PA(N)) and was dependent on aci dic pH for membrane insertion (optimal at pH 5.0), but not for sustain ed ion flux. The flux was reduced in the presence of several known cha nnel blockers: tetrabutyl-, tetrapentyl-, and tetrahexylammonium bromi des. PAN facilitated the membrane translocation of anthrax edema facto r under the same conditions that induced changes in membrane permeabil ity to ions. These results indicate that PA(N) permeabilizes cellular membranes under conditions that are believed to prevail in the endosom al compartment of toxin-sensitive cells; and they provide a basis for more detailed studies of the relationship between channel formation an d translocation of toxin effector moieties in vivo.