Synaptic vesicle
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In a neuron, synaptic vesicles, also called neurotransmitter vesicles, store the various neurotransmitters that are released during calcium-regulated exocytosis at the presynaptic terminal into the synaptic cleft of a synapse. They are essential for the propagation of nerve impulses between neurons and are constantly recreated by the cell.
Synaptic vesicles are made of a bilipid layer in which transport proteins specific to each type of neurotransmitters are inserted. Neurotransmitters are moved from the cytoplasm into the vesicles by active transport mechanisms involving an exchange of protons. The necessary proton gradient is created by hydrogen ATPase. The stoichiometry for the movement of different neurotransmitters into a vesicle is given in the following table.
| Neurotransmitter type(s) | Inward movement | Outward movement |
|---|---|---|
| norepinephrine, dopamine, histamine, serotonin and acetylcholine | neurotransmitter+ | 2 H+ |
| GABA and glycine | neurotransmitter | 1 H+ |
| glutamate | neurotransmitter- + Cl- | 1 H+ |