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. Author manuscript; available in PMC: 2010 Dec 29.
Published in final edited form as: Neuroscience. 2009 Sep 22;164(4):1546–1556. doi: 10.1016/j.neuroscience.2009.09.023

Figure 4.

Figure 4

EM analysis of photoconverted FM1-43 reveals that endosomes the size of single synaptic vesicles are retrieved in response to brief and prolonged stimulation. A, EM image of a mouse bipolar cell synaptic terminal loaded with FM1-43 in the presence of high K+. Cells were fixed and then photoconverted. Sections were not stained with uranyl acetate or lead citrate in order to preserve the native contrast between photoconverted and unlabeled vesicles. Dark spots indicate vesicles filled with FM1-43 (e.g., arrow). Scale bar represents 0.5 µm. B and C, Cell was fixed before removing high K+ from the bath. B, The plasma membrane appears crenellated with omega-shaped invaginations (arrows). Scale bar represents 0.25 µm. C, High magnification image of a budding vesicle. Scale bar represents 0.1 µm. D, EM image of two synaptic ribbons (r) in a cell that was patch clamped and then stimulated with a single 250-ms depolarization. The cell was fixed shortly thereafter and photoconverted. Arrow points to a synaptic vesicle that appears to have recycled back to the ribbon. Scale bar represents 0.25 µm. A larger structure appears adjacent to the other ribbon (arrow head). E, Three labeled vesicles docked at the membrane (arrow). Scale bar represents 0.125 µm. F, Size distribution of labeled vesicles in cells stimulated with high K+ (triangles) and a 250-ms depolarizing stimulus (circles). Mean diameter is ~33 nm. Vesicle size was measured in NIH Image.