Neither barium nor calcium prevents the inhibition by Bacillus thuringiensis δ‐endotoxin of sodium‐ or potassium gradient‐dependent amino acid accumulation by tobacco hornworm midgut brush border membrane vesicles

Rapid filtration assays were used to determine the effects of barium, calcium and an insecticidal δ‐endotoxin from Bacillus thuringiensis on sodium and potassium ion gradient dependent phenylalanine accumulation by brush border membrane vescles from the larval midgut of the tobacco hornworm (Manduca sexta). Neither barium nor calcium had a significant effect on sodium ion gradient dependent phenylalanine accumulation by the membrane vesicles. Both barium and calcium inhibited potassium ion gradient dependent phenylalanine accumulation by the membrane vesicles. B. thuringiensis δ‐endotoxin inhibited both sodium and potassium ion gradient dependent phenylalanine accumulation by the vesicles. Inhibition of both sodium and potassium ion gradient dependent phenylalanine accumulation increased similarly with increasing δ‐endotoxin inhibition of either sodium or potassium dependent phenylalanine accumulation by the vesicles.