The potent fungal metabolite cytochalasin D (CD) and cationized ferritin (CF) are used in combination to test for negative charge distribution on blebs (knobs). Two established human epithelial cell lines, WISH and HeLa, that display blebs in various phases of the cell cycle or under certain culture conditions (37,46) are investigated. CD alone, applied at a low concentration (1.0 μg/ml) and for a short time period (3 min), causes blebs to appear as the prevalent surface feature. These are filled mainly with free ribosomes. Additionally, feltlike mats, presumed to be disorganized, compacted microfilaments, are formed directly beneath the cell membrane. These are especially evident in the cortical cytoplasm below the blebs or bleb clusters. CF (0.345 mg/ml), applied for a 5-min period after CD administration (1.0 μg/ml) for 3 min, appears along the surface of microvilli, at the base of blebs, and in vesicles beneath the bleb clusters. In some cases, microfilaments (6 nm in diameter) are closely related to the vesicles. CF does not preferentially bind to the apical cell membrane of blebs. Above areas of the subplasmalemmal microfilaments, CF membrane binding is apparent, even under circumstances where the filaments are disorganized by cytochalasin treatment. These results seem to show the following: (a) bleb membranes are different from the remainder of the cell and do exhibit a loss of negative charge and (b) surface charge may be dependent on the presence or structural integrity of membrane-related 6-nm microfilaments.
- cationized ferritin
- cytochalasin D
- tissue culture
- transmission electron microscopy