Abstract
In order to determine the mechanism of action of the 27 kDa mosquitocidal δ-endotoxin of
Bacillus thuringiensis var.
israelensis we have studied its effects on the conductance of planar lipid bilayers. The toxin formed cation-selective channels in the bilayers, permeable to K
+ and Na
+ but not to
N-methylglucamine or Cl
−, showing very fast, cooperative opening and closing. Channel opening was greatly reduced in the presence of divalent cations (Ca
2+, Mg
2+) and the effect was reversed when these ions were removed. These results are consistent with our proposal that
B. thuringiensis toxins act by a mechanism of colloid-osmotic lysis.