VIDEO IMAGING ANALYSIS OF THE PLASMA-MEMBRANE PERMEABILIZING EFFECTS OF BACILLUS-THURINGIENSIS INSECTICIDAL TOXINS IN SF9 CELLS

The size and ionic selectivity of the pores formed by the insecticidal crystal protein Cry1C from Bacillus thuringiensis in the plasma membr ane of Sf9 cells, an established cell line derived from the fall armyw orm Spodoptera frugiperda, were analyzed with a video imaging techniqu e. Changes in the permeability of the membrane were estimated from the rate of osmotic swelling of the cells, In the presence of Cry1C, whic h is toxic to Sf9 cells, the permeability of the cell membrane to KCl and glucose increased in a dose-dependent manner. In contrast, Cry1Aa, Cry1Ab and Cry1Ac, toxins to which Sf9 cells are not susceptible, had no detectable effect. Pores formed by Cry1C allowed the diffusion of sucrose, but were impermeable to the trisaccharide raffinose. On the b asis of the hydrodynamic radii of these substances, the diameter of th e pores was estimated to be 1.0-1.2 nm. In the presence of salts, the rate of swelling of cells exposed to Cry1C was about equally influence d by the size of the anion as by that of the cation, indicating that t he ionic selectivity of the pores is low. (C) 1998 Elsevier Science B. V.