Role of endothelial cytoskeleton in high-permeability edema due to botulinum C2 toxin in perfused rabbit lungs.

The cytoskeleton of the endothelial cell has been suggested to regulate endothelial barrier function. We investigated the role of actin in the maintenance of pulmonary capillary integrity in perfused rabbit lungs. As a tool for selective perturbation of actin, we employed Clostridium botulinum C2 toxin, which is composed of a membrane translocation component (C2II) and a component (C2I) effecting ADP-ribosylation of nonmuscle G-actin. ADP-ribosylated actin no longer capable of polymerization but acts as a barbed end-capping protein, thereby effecting selective loss of the nonmuscle F-actin content. In buffer-perfused rabbit lungs, combined application of both toxin components (range 50 pg/ml-5 ng/ml C2I) resulted in a time- and dose-dependent increase in the capillary filtration coefficient (Kfc) with concomitant edema formation. Only 300:600 pg/ml C2I:II sufficed to induce a > 10-fold rise of Kfc values within 110 min. This severe lung permeability increase occurred in the absence of vasomotor responses and potassium release or lactate dehydrogenase release. Application of each single toxin component displayed markedly reduced efficacy. Similar to the C2 toxin effect, severe permeability increase without concomitant hemodynamic changes was evoked by cytochalasin D, known to possess F-actin-disrupting properties. Preloading of lung cells with phallacidin, which in opposition to C2 toxin decreases F-actin depolymerization, significantly reduced the C2 toxin-induced increase in vascular permeability. Electron microscopic examination of C2 toxin-poisoned lungs showed early, extensive endothelial cell attenuations, followed by disruptions of the endothelial layer and marked interstitial edema formation.(ABSTRACT TRUNCATED AT 250 WORDS)