Fig. 7.

Internalized vesicles at endocytic sites comprise discrete stable pools. Four muscles from one snake were stimulated in an SR101 bath (5 Hz; 30 sec), kept living in reptilian saline (4°C) without further stimulation for the time indicated, and then fixed. Shown are boutons from a typical terminal in each muscle. The labeled vesicles dispersed somewhat but remained in discrete pools, presumably near their original endocytic site. h, Hour;m, minute. Scale bar, 2 μm.