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.
Bibliographical noteFunding Information:
Acknowledgemenrs-This study was supportedin part by the Health SciencesR esearchC enterf unds (to YN), and by The Otto Myerhoff Drug ReceptorC enterfunds (to AS).