The Journal of Neuroscience, December 14, 2005, 25(50):11676-11683; doi:10.1523/JNEUROSCI.2972-05.2005
Previous Article | Next Article 
Cellular/Molecular
Activity-Dependent Acceleration of Endocytosis at a Central Synapse
Wei Wu,
Jianhua Xu,
Xin-Sheng Wu, and
Ling-Gang Wu
National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892
Accumulated evidence indicates the existence of rapid and slow endocytosis at many synapses. It has been proposed that rapid endocytosis is activated by intense stimulation when vesicle recycling needs to be speeded up to supply vesicles at hippocampal synapses. However, the evidence, as obtained with imaging techniques, which are somewhat indirect in indicating rapid endocytosis, is controversial. Furthermore, a slower time course of endocytosis is often found after more intense nerve activity, casting doubt on the role of rapid endocytosis at synapses. Here, we addressed this issue at a mammalian central synapse, the calyx of Held, using a capacitance measurement technique that provides a higher time resolution than imaging techniques. We found that rapid endocytosis with a time constant of
12 s was activated during intense nerve activity. Reducing the presynaptic calcium current or buffering the intracellular calcium with EGTA significantly inhibited rapid endocytosis, suggesting that calcium triggers rapid endocytosis. During intense stimulation, rapid endocytosis retrieved up to approximately eight vesicles per second per active zone, approximately eightfold larger than reported in the hippocampus, and thus played a dominant role during and within 3 s after intense stimulation. Slow endocytosis became dominant 3 s after intense stimulation likely because of the fall of the intracellular calcium level that deactivated rapid endocytosis. These results underscore the importance of calcium-triggered rapid endocytosis, which offers the nerve terminal the plasticity to speed up vesicle cycling during intense nerve activity.
Key words: synapse; calcium; plasticity; endocytosis; short-term facilitation; exocytosis
Received April 29, 2005;
revised October 11, 2005;
accepted November 1, 2005.