Quantification of the effect of Bacillus thuringiensis toxins on short-circuit current in the midgut of Bombyx mori

• Published in: Journal of insect physiology Vol. 41; no. 1; pp. 17 - 22
• Main Authors: Liebig, Baerbel, Stetson, David L., Dean, Donald H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1995
• Subjects: Bacillus thuringiensis; Bombycidae; Bombyx mori; CryIA; Insecticidal crystal proteins; Lepidoptera; δ-Endotoxin; Insecticidal crystal proteins; δ-Endotoxin; CryIA
• ISSN: 0022-1910; 1879-1611
• DOI: 10.1016/0022-1910(94)00093-V

We examined the abilities of two Bacillus thuringiensis insecticidal toxins, CryIAa and CryIAc, prepared from Escherichia coli-cloned gene products, to inhibit short-circuit current in midgut epithelia of Bombyx mori. Voltage-clamp studies were conducted on isolated midguts, measuring the inhibition of short-circuit current ( I SC) by trypsin-activated toxins. Three bathing solutions were compared and the medium of Chamberlin [(1990) J. exp. Biol. 150, 467–471] was found to maintain the highest I SC for the longest time. For CryIAa, a concentration range between 0.33 and 8.0 ng/ml resulted in inhibition of I SC at the rates of −0.91 μA/min (lag time, 9 min) and −7.13 μA/min (lag time, 4 min) respectively, showing a correlation between toxin concentration and inhibitory response. Concentrations greater than 1.6 ng/ml showed diminishing additional effects on the I SC response, indicating an approach to saturation. The lag times decreased with increasing concentration of toxin applied. For CryIAc, the lowest concentration that gave a response was 3.2 ng/ml (slope, −0.31 μA/min; lag time, 2 min). There also was a linear correlation between toxin concentration and response for CryIAc, but effective concentrations of CryIAc were approximately 2 orders of magnitude greater than those of CryIAa.