A close examination of the time course in B mori reveals that, prior to the decrease the pH peaks (Fig 1)
The mechanism mediating this rise is unknown, but may be a non-speciยฎc stress response to the force-feed procedure.
Luminal K activity is largely unaffected by Bt intoxication, but K activity in the haemolymph increases by more than 60%, abolishing even the small chemical gradient that existed under equilibrium conditions (Table 1). The source of the additional haemolymph K is uncertain, but may well be the midgut lumen itself. As the transmidgut PD decreases and luminal contents become acidiยฎed, it is possible that protein-bound K is released 8 and driven toward the haemolymph side until the activities in both compartments become equal.
Irreversible destruction of the midgut epithelium by Bt d-endotoxins is caused by a combination of cell alkalization 10 and colloid osmotic lysis. 11 Most insects susceptible to Bt, however, do not succumb directly to the endotoxin itself, but to the septicemia that follows, either from germinating Bt spores in the gut, if challenged with spore-crystal mixtures, or from other opportunistic pathogens that may be present in the gut.