Kinetics and regulation of fast endocytosis at hippocampal synapses.
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.
Department of Molecular and Cellular Physiology, Stanford Medical Center, California 94305, USA.
J
J
Klingauf
E T
ET
Kavalali
R W
RW
Tsien
D000818:Animals; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000378:metabolism; D006624:Hippocampus / Q000502:physiology*; D007700:Kinetics; D008959:Models, Neurological; D017729:Presynaptic Terminals / Q000502:physiology; D047428:Protein Kinase Inhibitors; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D019311:Staurosporine / Q000494:pharmacology; D013569:Synapses / Q000502:physiology*; D013570:Synaptic Membranes / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology
D004791:Enzyme Inhibitors; C113793:FM 1 84; C073804:FM1 43; C086686:FM2 10; D005456:Fluorescent Dyes; D047428:Protein Kinase Inhibitors; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D019311:Staurosporine; D002118:Calcium