A 28,000 MOL-WT TOXIN FROM BACILLUS-THURINGIENSIS ISRAELENSIS INDUCESCATION-TRANSPORT IN RAT MUSCLE CULTURES

The mechanism by which the Bacillus thuringiensis israelensis (Bti) 28 ,000 mel. wt toxin exerts its effect on mature muscle cultures was exa mined. The toxin inhibited Na+/K+-ATPase activity as revealed by Rb-86 influx. A 50% inhibition of Na+/K+-ATPase activity was obtained with 0.2 mu g/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 mu g/ml. A considerable release of Rb-86 was obtained by doses greater than 0.2 mu g/ml. The Rb-86 release was also time and dose dependent. This eff ect is probably non-specific, since Ca-45 influx is also accelerated b y toxin-treated cultures. Pre-incubation of the toxin with phosphotidy lserine (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 d oses it causes non-specific permeability of the sarcolemma.