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Updated: Aug 8, 2026

Measuring Synaptic Vesicle Endocytosis in Cultured Hippocampal Neurons
Published on: September 4, 2017
Discrete residues in the c(2)b domain of synaptotagmin I independently specify endocytic rate and synaptic vesicle
Kira E Poskanzer1, Richard D Fetter, Graeme W Davis
1Department of Biochemistry and Biophysics, University of California, San Francisco, Rock Hall, 1550 Fourth Street, Box 2822, San Francisco, California 94158, USA.
Abstract:
It has been demonstrated that synapses lacking functional synaptotagmin I (Syt I) have a decreased rate of synaptic vesicle endocytosis. Beyond this, the function of Syt I during endocytosis remains undefined. Here, we demonstrate that a decreased rate of endocytosis in syt(null) mutants correlates with a stimulus-dependent perturbation of membrane internalization, assayed ultrastructurally. We then separate the mechanisms that control endocytic rate and vesicle size by mapping these processes to discrete residues in the Syt I C(2)B domain. Mutation of a poly-lysine motif alters vesicle size but not endocytic rate, whereas the mutation of calcium-coordinating aspartate residues (syt-D3,4N) alters endocytic rate but not vesicle size. Finally, slowed endocytic rate in the syt-D3,4N animals, but not syt(null) animals, can be rescued by elevating extracellular calcium concentration, supporting the conclusion that calcium coordination within the C(2)B domain contributes to the control of endocytic rate.
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