A large pool of releasable vesicles in a cortical glutamatergic synapse.
To probe exocytosis at a cortical glutamatergic synapse, we made capacitance measurements in whole-cell recorded hippocampal mossy fiber terminals. Evaluation of different methods by using a morphology-based equivalent electrical model revealed that quantitative capacitance measurements are possible in this presynaptic structure. Voltage pulses leading to presynaptic Ca2+ inflow evoked large capacitance signals that showed saturation with increasing pulse duration. The mean peak capacitance increase was 100 fF, corresponding to a pool of approximately 1,400 releasable vesicles. Thus hippocampal mossy fiber synapses have a vesicular "maxipool." Large pool size and rapid vesicle recycling may underlie the uniquely large extent of activity-dependent plasticity in this synapse.
Hallermann
Stefan
S
Physiologisches Institut, Universität Freiburg, D-79104 Freiburg, Germany.
Pawlu
Christian
C
Jonas
Peter
P
Heckmann
Manfred
M
D000818:Animals; D025802:Electric Capacitance; D004594:Electrophysiology; D004705:Endocytosis; D005089:Exocytosis; D066298:In Vitro Techniques; D008959:Models, Neurological; D019599:Mossy Fibers, Hippocampal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D022142:Secretory Vesicles / Q000502:physiology*; D009435:Synaptic Transmission