title: Mechanism of inhibition of active potassium transport in isolated midgut of Manduca sexta by Bacillus thuringiensis endotoxin.
abstract: After incubation at pH 10 or higher, Bacillus thuringiensis spores and endotoxin, at concentrations above 0.1 IU/ml, affected transport parameters in the isolated midgut of Manduca sexta larvae. (Toxic activity was lost during roughly 1 week at pH 11.) About 60% of the short-circuit current was inhibited, and the remainder was reversibly inhibited by anoxia. Electrical resistance was reduced by about 55% and oxygen uptake stimulated by about 30%. Influx of potassium from blood-side to lumen-side ('active' flux) was unaffected but flux in the reverse direction was nearly tripled. These results suggest that hydrolysis of the toxin yields an inhibitor of potassium transport, presumably a polypeptide. It is argued that inhibition is not primarily by uncoupling of oxidative phosphorylation, but instead by interference with an active depression of the efflux of potassium from lumen-side to blood-side.
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis; D001427:Bacterial Toxins / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004731:Endotoxins / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007422:Intestines / Q000187:drug effects; D007915:Lepidoptera / Q000502:physiology*; D009036:Moths / Q000502:physiology*; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D004731:Endotoxins; D011188:Potassium