The initial stages in the action of an insecticidal delta-endotoxin of XXXX on the epithelial cells of the malpighian tubules of the insect, Rhodnius prolixus.

@entity177 @entity204 @entity25551 @entity73261
The effects of the 27 X 10(3) Mr insecticidal delta-endotoxin from @entity25551 have been studied using, as a model system, isolated insect Malpighian tubules. At all concentrations of the @entity73261 higher than 1 microgram ml-1 (4 X 10(-8) moll-1) applied to the outer surface of the tubules, fluid secretion failed within about 30 min. Except at very high concentrations, where @entity177 always takes at least 30 s, there was an inverse relationship between the concentration of @entity73261 and the time of @entity177 of @entity73261 -treated tubules. During exposure to @entity73261 , the tubules were initially unaffected for a relatively long period and then rapid @entity177 occurred. If the tubules were removed into @entity73261 -free saline just before @entity177 would have occurred, fluid secretion remained normal for at least 2 h, but on return to the origin @entity73261 -containing saline @entity177 was almost immediate. The @entity73261 was found not to bind to the basement membrane. Ultrastructural changes became evident as tubule @entity177 occurred. These initially involved modifications to the basal side of the cells, but later also to the luminal microvilli. Intercellular junctions became disassociated and cytoplasmic vacuolization occurred. The population of intramembranous particles in the basal membranes became reduced with time. Our findings suggest the following hypothesis for the initial stages in the interaction of the @entity73261 with the tubules. @entity73261 molecules attach to the accessible cell membranes progressively and irreversibly. They do not readily associate by diffusing laterally in the membrane, so that toxic effects develop only when sufficiently large numbers of them attach close together. The molecules may then associate in some way as a complex, perhaps forming a pore in the membrane. Relatively few such pores lead rapidly to cell @entity177 and @entity204 .
