Independent Alterations in Cell Shape and Intramembranous Particle Topography Induced by Cytochalasin B and Colchicine in Normal and Transformed Cells

Native differences in cell shape and plasma membrane organization in contact-innibited and transformed cells and the effects of cytochalasin B and colchicine on these cells have been examined by scanning electron microscopy and freeze fracture-electron microscopy. Confluent BALB/c 3T3 cells show a flat, polygonal shape with limited cell overlapping, some microvilli, and plasma membranes with an aggregated distribution of intramembranous particles. Simian virus 40-transformed BALB/c 3T3 cells, by contrast, have a pleomorphic, bipolar spindle shape, extensive cell overlapping, more numerous surface projections, and a random distribution of intramembranous particles. Treatment of 3T3 and SV3T3 cells with 10-6 m colchicine produced changes in cell shape and induced intramembranous particle aggregation in SV3T3 cells but did not significantly affect the freeze fracture morphology of 3T3 plasma membranes. Treatment of 3T3 and SV3T3 cells with cytochalasin B (1 μg/ml) also produced marked changes in cell shape and induced intramembranous particle disaggregation in 3T3 cells, but it did not affect intramembranous particle distribution in SV3T3 cells. Lower doses of colchicine (10-9 m) or cytochalasin B (1 to 50 ng) modulated intramembranous particle distribution in transformed and normal 3T3 cells, respectively, without seriously affecting cell shape. These results are interpreted to suggest that modulation of cell shape or cell surface topography and intramembranous particle distribution are separable phenomena.