Figure 7.

Clathrin and synaptic vesicle recycling. (a) Resting control culture. Clathrin-coated pits and vesicles are seen only occasionally, whereas empty clathrin baskets (arrowheads) are more numerous. (b) K⁺-depolarized control culture. Clathrin-coated pits and vesicles (arrows) are seen commonly; empty clathrin baskets are rare. Note the electron lucent matrix of mitochondria (asterisks) in cultures fixed during stimulation. (c) Resting TeNT-blocked culture. Clathrin-coated pits and vesicles are almost never seen although empty clathrin baskets are found easily. (d) K⁺-depolarized TeNT-blocked culture. K⁺ stimulation causes a change in the density of the mitochondrial matrix, but no noteworthy change in the distribution of synaptic vesicles at the active zone or frequency of clathrin baskets or clathrin-coated membranes. (e) Resting BoNT A–blocked culture. This culture appears similar to the TeNT-blocked culture in the absence of clathrin-coated membranes and the persistence of empty clathrin baskets. (f) K⁺-depolarized BoNT A–blocked culture. This culture appears more similar to the stimulated control than to the stimulated TeNT-blocked culture. Empty clathrin baskets have all but disappeared and clathrin-coated membranes can be found. Toxin concentrations as in Fig. 5. Bar, 0.5 μm.