Long-lasting fusion pore opening during exocytosis of a MT1-MMP–containing endosome. MDA-MB-231 cells expressing MT1-MMPpHLuorin were cultured on a layer of Cy3-labeled type I collagen fibers and subjected to a shift of the external pH alternating between 7.4 and 5.5. A MT1-MMP–positive endosome that undergoes exocytosis is circled in yellow. An adjacent region of the plasma membrane is circled in purple. Cells were imaged by wide-field videomicroscopy (IX71; Olympus). Images were taken every 2 s for 292 s (indicated time is in min:s).
