Release of endosomal content induced by plasma membrane tension: Video image intensification time lapse analysis

Abstract Rhodamine-labeled vinculin microinjected into chicken embryo fibroblasts and rhodamine-labeled α 2 -macroglobulin added to the fibroblast culture medium were sequestered in endocytotic vesicles and digested. When a sealed microcapillary coated with fibronectin or polylysine was attached to the fibroblasts and pulled at speeds of 100–200 μm/h, stretching the plasma membrane, a variable fraction of the endosomes released the rhodamine label. Release from individual vesicles was rapid, reaching completion in less than 30 to 120 s. The microfilament disrupting agent cytochalasin B prevented release, as did the microtubule stabilizing drug taxol. Colcemide, which disrupts microtubules, did not inhibit the release. Release was dependent on extracellular calcium, as it was prevented by 10 m M EGTA in the incubation medium. We postulate that opening of vesicular channels consequent to centripetal transmission of tension generated in the plasma membrane along microfilaments may be a mechanism of release of endosomal content.