Freeze-fracture ultrastructural alterations induced by filipin, pimaricin, nystatin and amphotericin B in the plasma membranes of Epidermophyton, Saccharomyces and red blood cells. A proposal of models for polyene·ergosterol complex-induced membrane lesions

Abstract

The effects of chemically different polyenes on fungal membranes Epidermophyton floccosum, a human pathogenic fungus, and Saccharomyces cerevisiae and human red blood cell membranes were studied by freeze-fracture electron microscopy in order to elucidate the interaction of these antibiotics with ergosterol. Each type of neutral, small amphoteric and large amphoteric polyenes produces a distinct morphological effect on the fungal membranes: 1. (1) Pit formation type. Filipin, a neutral polyene, produces 250–300 Å diameter “pits” or “invagination” both in ergosterol-containing fungal plasma membranes and cholesterol-containing red blood cell ghost membranes. 2. (2) Network particle aggregation type. The small amphoteric polyene, pimaricin, produces a network of membrane particle aggregation which encloses 1000 Å diameter particle-free areas in fungal membranes. These areas are slightly elevated toward the outside of the cell. 3. (3) Random particle aggregation type. The large amphoteric polyenes, amphotericin B and nystatin, cause a random segregation of the fungal plasma membrane and the red blood cell ghost membranes into particle-free and aggregated areas. It is concluded that these morphological differences are due to different mechanisms of polyene-sterol interactions in which the different size of the macrolide ring in the antibiotic structure may be involved. Since all of these antibiotics, except filipin, cause no alterations on whole red blood cells detectable by negative staining and freeze-fracture electron microscopy, it is possible that they have a higher affinity to ergosterol than cholesterol in membranes.