Figure 3.

N2A cells in the presence of medium (M) with and without CaCl₂ (Ca) or PA63 in the presence or absence of CaCl₂. (A) More cells (intact nuclei stained blue with DAPI) became permeable to PI (red stain) in the presence of PA63 compared with cells in medium indicating compromised ability to reseal their membranes; the addition of exogenous CaCl₂ had a protective effect. PA63 increased percent cells permeable to PI by almost 2× (*P < .05). (B) The addition of CaCl₂ prevented increased permeability to PI, as did the addition of antibodies to anthrax (AA) (**P < .01). DAPI indicates 4′,6-diamidino-2-phenylindole; N2A cells, neuroblastoma 2A cells; PA63, anthrax protective antigen 63; PI, propidium iodide.