Delta-endotoxins induce cation channels in Spodoptera frugiperda brush border membranes in suspension and in planar lipid bilayers.
Membrane potential measurements using a fluorescent dye indicated that two specific toxins active against Spodoptera frugiperda larvae (CryIC and CryID) cause immediate permeability changes in midgut epithelial brush border membrane vesicles (BBMV). The initial response and the sustained permeability change are cationic, not very K+ selective, and occur at in vivo lethal doses (nM). The toxin response has a different ion selectivity and is more sensitive to Ba2+ than the intrinsic cation permeability of BBMV. Experiments incorporating BBMV into planar lipid bilayers (PLB) demonstrated that these vesicles contain cation channels (31, 47 and 76 pS). A 2-40 fold conductance increase was induced by nM concentrations of toxin in PLB containing BBMV. Cationic single channel transitions of 50, 106, 360 and 752 pS were resolved. Thus, Bacillus thuringiensis delta-endotoxins induce an increase in cation membrane permeability involving ion channels in BBMV-containing functional receptors.
Lorence
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Instituto de Biotecnologia, Universidad Nactional Autónoma de México, Cuernavaca, Mor.
Darszon
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Díaz
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C
Liévano
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Quintero
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R
Bravo
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D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000494:pharmacology*; D001427:Bacterial Toxins; D004731:Endotoxins / Q000494:pharmacology*; D006460:Hemolysin Proteins; D066298:In Vitro Techniques; D007422:Intestines / Q000187:drug effects*; D015640:Ion Channel Gating; D007473:Ion Channels; D007814:Larva; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli; D018411:Spodoptera
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; C030956:insecticidal crystal protein, Bacillus Thuringiensis