Estimation of electrophysiological parameters derived from in vitro response of insect midguts to Bacillus thuringiensis Cry1A proteins

Abstract

Epithelial voltage clamping of insect midguts were conducted to estimate electrophysiological parameters describing insecticidal activity of Cry proteins in vitro. Maximal short-circuit current inhibition rates (I sc-max) of Cry1Aa, Cry1Ab, and Cry1Ac were estimated from the Michaelis-Menten fit of toxin concentration and short-circuit current inhibition rates derived from toxin-treated midguts of Manduca sexta and Lymantria dispar. Cry1Aa Isc-max was faster in M. sexta (146.8±43.2 μA min-1 cm-2) as compared to L. dispar (67.50±17.8 μA min-1 cm-2) midgut. However, Cry1Aa Isc-max in L. dispar was faster as compared to Cry1Ab (49.4±1.7 μA min-1 cm-2) and Cry1Ac (23.1±1.8 μA min-1 cm-2). The apparent Cry1Aa macroconductance estimated from current-voltage plots was faster in M. sexta (260±19.8 mSiemens) than in L. dispar (160±28.0 mSiemens). In addition, the short-circuit current inhibition rates in insect midgut responded positively to increasing concentration of Bacillus thuringiensis Cry1A toxins and begin to approach saturation at 3 nM. Considering the labor input in conducting larval bioassays, Isc-max and/or toxin macroconductance could be useful in predicting in vivo Cry protein insecticidal activity.

Source or Periodical Title

Philippine Agricultural Scientist

ISSN

317454

Page

254-258

Document Type

Article

Subject

Bacillus thuringiensis, Cry1A proteins, Insect midgut, Short-circuit current

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