Maddrell S H, Lane N J, Harrison J B, Overton J A, Moreton R B
AFRC Unit of Insect Neurophysiology and Pharmacology, Department of Zoology, Cambridge, England.
J Cell Sci. 1988 May;90 ( Pt 1):131-44. doi: 10.1242/jcs.90.1.131.
The effects of the 27 X 10(3) Mr insecticidal delta-endotoxin from Bacillus thuringiensis var. israelensis have been studied using, as a model system, isolated insect Malpighian tubules. At all concentrations of the toxin 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 failure always takes at least 30 s, there was an inverse relationship between the concentration of toxin and the time of failure of toxin-treated tubules. During exposure to toxin, the tubules were initially unaffected for a relatively long period and then rapid failure occurred. If the tubules were removed into toxin-free saline just before failure would have occurred, fluid secretion remained normal for at least 2 h, but on return to the origin toxin-containing saline failure was almost immediate. The toxin was found not to bind to the basement membrane. Ultrastructural changes became evident as tubule failure 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 toxin with the tubules. Toxin 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 failure and death.
以分离出的昆虫马氏管作为模型系统，对苏云金芽孢杆菌以色列变种中27×10³Mr的杀虫δ-内毒素的作用进行了研究。当毒素以高于1微克/毫升（4×10⁻⁸摩尔/升）的所有浓度施加于马氏管外表面时，液体分泌在约30分钟内停止。除了在非常高的浓度下（此时分泌停止总是至少需要30秒），毒素处理过的马氏管中，毒素浓度与分泌停止时间呈反比关系。在接触毒素期间，马氏管最初在较长一段时间内未受影响，然后迅速停止分泌。如果在分泌停止即将发生之前将马氏管移入无毒素的盐溶液中，液体分泌至少2小时仍保持正常，但当再移回到原来含毒素的盐溶液中时，分泌几乎立即停止。发现该毒素不与基底膜结合。随着马氏管分泌停止，超微结构变化变得明显。这些变化最初涉及细胞基底侧的改变，但后来也涉及管腔微绒毛的改变。细胞间连接解离，细胞质空泡化。基底膜中膜内颗粒的数量随时间减少。我们的研究结果为毒素与马氏管相互作用的初始阶段提出了以下假说。毒素分子逐渐且不可逆地附着于可及的细胞膜上。它们不容易通过在膜中侧向扩散而结合，因此只有当足够大量的毒素分子紧密附着在一起时才会产生毒性作用。然后这些分子可能以某种方式结合形成复合物，也许在膜中形成一个孔。相对较少的这样的孔会迅速导致细胞停止分泌和死亡。
