A 28,000 mol. wt toxin from Bacillus thuringiensis israelensis induces cation transport in rat muscle cultures

The mechanism by which the Bacillus thuringiensis israelensis (Bti) 28,000 mol. wt toxin exerts its effect on mature muscle cultures was examined. The toxin inhibited Na⁺ K⁺-ATPase activity as revealed by ⁸⁶Rb influx. A 50% inhibition of Na⁺ K⁺-ATPase activity was obtained with 0.2 μg/ml of the toxin. The inhibition was time and dose dependent, and it was reversible with low doses of the toxin (up to 0.2 μg/ml. A considerable release of ⁸⁶Rb was obtained by doses greater than 0.2 μg/ml. The ⁸⁶Rb release was also time and dose dependent. This effect is probably non-specific, since ⁴⁵Ca influx is also accelerated by toxin-treated cultures. Pre-incubation of the toxin with phosphotidylserine (PS) antagonized the toxin. It is concluded that the toxin is a hydrophobic protein which interacts with the membrane. In low doses this interaction reduces the activity of the sodium pump and in high doses it causes non-specific permeability of the sarcolemma.