Exo-endocytosis in isolated peptidergic nerve terminals occurs in the sub-second range |
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Authors: | Gerd Knoll Helmut Plattner Jean J Nordmann |
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Institution: | (1) Centre de Neurochemie-UPR 416, C.N.R.S., 5 rue Blaise Pascal, F-67084 Strasborg Cedex, France;(2) Universität Konstanz Fakultät für Biologie, Postfach 5560, D-7750 Konstanz, Germany |
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Abstract: | Exo- and endocytotic processes induced by depolarization of isolated neurosecretory nerve terminals show a close temporal correlation, which suggests a short time of integration of the neurosecretory granule membrane with the plasma membrane. In order to determine minimal time requirements for exocytosis-coupled endocytosis to occur, we have analyzed by electron microscopy uptake of horserdish peroxidase (HRP) as a fluid phase marker at the onset of depolarization. We have applied rapid mixing and sampling (quenched flow) to assess events in subsecond time peroids after stimulation. A significant number of labelled endocytotic vacuoles was observed during the first second of depolarization. This number then further increased by a factor of about 2 (within 5 s) and 4 (within 50s). Thus, as for exocytosis, the rate of endocytosis decreased considerably during prolonged stimulation. These data indicate i) that a substantial proportion of secretory granules undergoes exocytosis very shortly after stimulation, and ii) that, following exocytosis, the minimal time required for consecutive membrane retrieval is in the sub-second range. |
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Keywords: | Electron microscopy secretion neuropeptides exocytosis endocytosis |
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