Patch-clamp study of the apical membrane of the midgut of Manduca sexta larvae: direct demonstration of endogenous channels and effect of a Bacillus thuringiensis toxin.
The patch-clamp technique was applied to the apical membrane of epithelial midgut cells of a lepidoptera, Manduca sexta L. Access to the apical membrane, the main target site of Bacillus thuringiensis (Bt) toxins, was achieved by using freshly isolated larval midgut preparations mounted onto holding glass pipettes. The epithelial cells retained their functional integrity, as evidenced by the magnitude of intracellular potentials recorded with microelectrodes. With standard 32 mM K(+) solution in the bath and the patch-clamp pipette, endogenous channel activity was detected in about 50% of experiments, mainly in moulting larvae and larvae that had been kept at reduced temperature for at least two days prior to the experiments. In both cell-attached and inside-out patch-clamp configurations, different types of channel were observed, with conductances varying between about 5 and 50 pS and different conducting properties. Addition of trypsin-activated Cry1Ac Bt toxin in the patch-clamp pipette triggered, after a delay, large conductances of a few nanosiemens. This is the first study allowing exploration, in the intact midgut, of the properties of apical membrane channels and the direct interaction between the apical membrane of epithelial cells and pathogenic agents such as Bt toxins.
Peyronnet
Olivier
O
Biocontrol Network and Groupe d'Etude des Protéines Membranaires, Université de Montréal, Montreal, Que. H3C 3J7, Canada.
Noulin
Jean-François
JF
Laprade
Raynald
R
Schwartz
Jean-Louis
JL
D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000633:toxicity*; D001427:Bacterial Toxins / Q000633:toxicity*; D004064:Digestive System / Q000378:metabolism*; D004594:Electrophysiology; D004731:Endotoxins / Q000633:toxicity*; D004848:Epithelium / Q000378:metabolism; D006460:Hemolysin Proteins; D007814:Larva / Q000378:metabolism; D018402:Manduca / Q000378:metabolism*; D008839:Microelectrodes; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D015221:Potassium Channels; C030956:insecticidal crystal protein, Bacillus Thuringiensis