Evaluation of the polyene antibiotic filipin as a cytochemical probe for membrane cholesterol

Distribution of the filipin-cholesterol complexes has been studied by freeze-fractures techniques. While filipin-cholesterol complexes are formed in fixed as well as unfixed cells, the distribution of the complexes varies with fixation. Furthermore, filipin induces dramatic rearrangement of intramembrane particles in unfixed, but not in fixed, cells. Examination of thin sections of filipin-treated cells shows that filipin alone induces substantial cellular damage, while filipin treatment simultaneous to fixation or following fixation does not cause noticeable damage. For filipin to be an effective cytochemical probe of membrane structure, cellular damage must be minimized; this is best achieved by treating cells with filipin following glutaraldehyde fixation.