Clathrin-coated vesicles in mouse bipolar neurons. A, Serial EM sections of a cell that was patch-clamped and held at −60 mV, then fixed ~30s after the patch pipette was removed. The left panel shows a synaptic ribbon (arrow head). The middle panel is the next section in the series and shows a cytoplasmic clathrin-coated vesicle (arrow) adjacent to the synaptic ribbon (arrow head). The panel on the right is a higher-magnification view of the coated vesicle in the middle panel. Another structure, also visible in the left and middle panels, seems to be budding from the membrane (arrow head). B, EM image of a clathrin-coated vesicle budding from the plasma membrane. The cell was stimulated with high K+ for ~30 s and fixed before removing high K+ from the bath. C, EM image of multiple clathrin coated vesicles in the process of budding. Same cell as in A. Scale bars in A–C represent 0.125 µm.