Delta endotoxin inhibits Rb+ uptake, lowers cytoplasmic pH and inhibits a K+-ATPase in Manduca sexta CHE cells.

Delta endotoxin, a 68 kilodalton protein isolated from Bacillus thuringiensis spp. Kurstaki, is a potent entomocidal agent that alters a K+ current across midgut tissue of many phytophagous insects. This toxin completely inhibited the vanadate-sensitive 86Rb+ uptake and mimicked the vanadate-induced decrease in cytosolic pH in a cell line (CHE) originating from Manduca sexta embryonic tissue. The toxin also inhibited a K+-sensitive-ATPase in the plasma membranes isolated from these cells. Using the K+-sensitive-ATPase substrate p-nitrophenyl phosphate, delta endotoxin was found to have a Ki of 0.4 microM. These data suggest that the toxin inhibits a K+-ATPase responsible for 86Rb+ uptake in the CHE cells. The relationship between the toxin inhibition of K+-ATPase and toxin-altered K+ current is discussed.