Kinetics and regulation of fast endocytosis at hippocampal synapses

Abstract

Presynaptic nerve terminals often contain as few as a hundred vesicles and so must recycle them soon after exocytosis to preserve synaptic transmission and presynaptic morphology during repetitive firing. The kinetics and mechanisms of vesicular endocytosis and repriming have therefore been studied. Vesicles in hippocampal nerve terminals can become available to release their contents within approximately 40 s of the previous round of exocytosis. Studies using the styryl dye FM1-43 have estimated the time constant for endocytosis as approximately 20-30 s at least half of the total recycling time, which is much slower than endocytosis in other secretory systems. It seems paradoxical that the neurosecretory terminals that could benefit the most from rapid endocytosis do not use such a mechanism. Here we demonstrate the existence of fast endocytosis in hippocampal nerve terminals and derive its kinetics from fluorescence measurements using dyes with varying rates of membrane departitioning. The rapid mode of vesicular retrieval was much faster after exposure to staurosporine or elevated extracellular calcium. Thus hippocampal synapses take advantage of efficient mechanisms for endocytosis, and their vesicular retrieval is subject to modulatory control.

Properties of fast endocytosis at hippocampal synapses

“…If, however, membrane is retrieved more rapidly at the sites of exocytosis (`fast'), some fraction of dye will be trapped in freshly retrieved vesicles, which will eventually recycle back to the primed pool. Reprinted by permission of Nature (Klingauf et al 1998), copyright (1998) Macmillan Magazines Ltd.…”

“…The fast endocytotic mechanism we report here possesses several hallmarks of the`kiss and run' pathway proposed by Bruno Ceccarelli and colleagues (Ceccarelli et al 1973;Ceccarelli & Hurlbut 1980; for review, see Fesce et al 1994). This is a more complete and explanatory presentation of work reported in a recent paper (Klingauf et al 1998). …”

“…Lond. B (1999) Reprinted by permission of Nature (Klingauf et al 1998), copyright (1998) Macmillan Magazines Ltd.…”

Imaging Synaptic Vesicle Recycling by Staining and Destaining Vesicles with FM Dyes

“…However, if the process of endocytosis is faster than the departitioning of the dye from the membrane, proportionally more FM2-10 should be released, which was indeed the observed result. Furthermore, the more lipophilic FM1-84 was released even more slowly than FM1-43 (Klingauf et al 1998), suggesting that hippocampal boutons rely on fast vesicle recovery. One should note, however, that this differential release of dyes is not necessarily a general phenotype for all preparations (see the frog NMJ, Richards et al 2000).…”

“…One experiment focused on the release of different FM dyes from vesicles during destaining (Klingauf et al 1998;Pyle et al 2000; Fig. 2A).…”