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J. Biol. Chem., Vol. 280, Issue 44, 37278-37288, November 4, 2005

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Properties of Synaptic Vesicle Pools in Mature Central Nerve Terminals^*

Anthony C. Ashton and Yuri A. Ushkaryov1

From the Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom and the Department of Biological Sciences, University of Central Lancashire, Preston PR1 2HE, United Kingdom

Readily releasable and reserve pools of synaptic vesicles play different roles in neurotransmission, and it is important to understand their recycling and interchange in mature central synapses. Using adult rat cerebrocortical synaptosomes, we have shown that 100 mosM hypertonic sucrose caused complete exocytosis of only the readily releasable pool (RRP) of synaptic vesicles containing glutamate or -aminobutyric acid. Repetitive hypertonic stimulations revealed that this pool recycled (and reloaded the neurotransmitter from the cytosol) fully in <30 s and did so independently of the reserve pool. Multiple rounds of exocytosis could occur in the constant absence of extracellular Ca²⁺. However, although each vesicle cycle includes a Ca²⁺-independent exocytotic step, some other stage(s) critically require an elevation of cytosolic [Ca²⁺], and this is supplied by intracellular stores. Repetitive recycling also requires energy, but not the activity of phosphatidylinositol 4-kinase, which maintains the normal level of phosphoinositides. By varying the length of hypertonic stimulations, we found that 70% of the RRP vesicles fused completely with the plasmalemma during exocytosis and could then enter silent pools, probably outside active zones. The rest of the RRP vesicles underwent very fast local recycling (possibly by kiss-and-run) and did not leave active zones. Forcing the fully fused RRP vesicles into the silent pool enabled us to measure the transfer of reserve vesicles to the RRP and to show that this process requires intact phosphatidylinositol 4-kinase and actin microfilaments. Our findings also demonstrate that respective vesicle pools have similar characteristics and requirements in excitatory and inhibitory nerve terminals.

Received for publication, April 15, 2005 , and in revised form, August 9, 2005.

^* This work was supported by a senior European research fellowship and Project Grant GR074359MA (to Y. A. U.) from the Wellcome Trust. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Div. of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, UK. Tel.: 44-20-7594-5237; Fax: 44-20-7594-5207; E-mail: y.ushkaryov{at}imperial.ac.uk.

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