The locomotion of fibroblasts in culture. IV. Electron microscopy of the leading lamella

Electron microscopy of vertical longitudinal sections of chick heart fibroblasts moving on an Araldite substratum show that the cell approaches close to the substratum in localised regions which in all occupy about one quarter of the area of the lower surface of the leading lamella; and the cytoplasm adjacent to these regions of close approach, which we suggest are adhesions, tends to form electron-dense plaques containing longitudinal filaments. There are suggestions that the plaques are linked up to the fibrillar system of the cell. The lamellipodia (which form the ruffles) are of rather constant thickness, and contain a faintly fibrillar cytoplasm devoid of major cell organelles.