Daugelavicius R, Bakiene E, Bamford D H
Department of Biochemistry and Biophysics, Vilnius University, Ciurlionio 21, LT-2009 Vilnius, Lithuania.
Antimicrob Agents Chemother. 2000 Nov;44(11):2969-78. doi: 10.1128/AAC.44.11.2969-2978.2000.
The effects of polymyxin B (PMB) on the Escherichia coli outer (OM) and cytoplasmic membrane (CM) permeabilities were studied by monitoring the fluxes of tetraphenylphosphonium, phenyldicarbaundecaborane, and K(+) and H(+) ions. At concentrations between 2 and 20 microgram/ml, PMB increased the OM permeability to lipophilic compounds and induced a leakage of K(+) from the cytosol and an accumulation of lipophilic anions in the cellular membranes but did not cause the depolarization of the CM. At higher concentrations, PMB depolarized the CM, forming ion-permeable pores in the cell envelope. The permeability characteristics of PMB-induced pores mimic those of bacteriophage- and/or bacteriocin-induced channels. However, the bactericidal effect of PMB took place at concentrations below 20 microgram/ml, indicating that this effect is not caused by pore formation. Under conditions of increased ionic strength, PMB made the OM permeable to lipophilic compounds and decreased the K(+) gradient but was not able to depolarize the cells. The OM-permeabilizing effect of PMB can be diminished by increasing the concentration of Mg(2+). The major new findings of this work are as follows: (i) the OM-permeabilizing action of PMB was dissected from its depolarizing effect on the CM, (ii) the PMB-induced ion-permeable pores in bacterial envelope were registered, and (iii) the pore formation and depolarization of the CM are not obligatory for the bactericidal action of PMB and dissipation of the K(+) gradient on the CM.
通过监测四苯基鏻、苯基二碳硼烷以及K⁺和H⁺离子的通量，研究了多粘菌素B（PMB）对大肠杆菌外膜（OM）和细胞质膜（CM）通透性的影响。在2至20微克/毫升的浓度范围内，PMB增加了外膜对亲脂性化合物的通透性，诱导K⁺从胞质溶胶中泄漏以及亲脂性阴离子在细胞膜中积累，但并未导致细胞质膜去极化。在更高浓度下，PMB使细胞质膜去极化，在细胞包膜中形成离子通透孔。PMB诱导的孔的通透性特征类似于噬菌体和/或细菌素诱导的通道。然而，PMB的杀菌作用发生在浓度低于20微克/毫升时，表明这种作用不是由孔的形成引起的。在离子强度增加的条件下，PMB使外膜对亲脂性化合物具有通透性并降低了K⁺梯度，但无法使细胞去极化。增加Mg²⁺的浓度可减弱PMB的外膜通透作用。这项工作的主要新发现如下：（i）将PMB的外膜通透作用与其对细胞质膜的去极化作用区分开来；（ii）记录了PMB在细菌包膜中诱导的离子通透孔；（iii）细胞质膜的孔形成和去极化对于PMB的杀菌作用以及细胞质膜上K⁺梯度的消散并非必不可少。
