Presynaptic glutamate transporter

Glutamate removal. Glutamate s actions ate stopped not by enzymatic breakdown, as in other neurotransmitter systems, but by removal by two transport pumps. The first of these pumps is a presynaptic glutamate transporter, which works as do all the other neurotransmitter transporters already discussed for monoamine neurotransmitter systems such as dopamine, norepinephrine, and serotonin. The second transport pump, located on nearby glia, removes glutamate from the synapse and terminates its actions there. Glutamate removal is summarized in Figure 10—22. 

Wersinger E., Schwab Y., Sahel J. A., Rendon A., Pow D. V., Picaud S., and Roux M. J. (2006). The glutamate transporter EAAT5 works as a presynaptic receptor in mouse rod bipolar cells. J. Physiol. 

Several of the neurotransmitters are small-molecule amines such as dopamine, serotonin, epinephrine, and norepinephrine. These neurotransmitters are synthesized in the cytoplasm of the axon terminal and subsequently transported into and stored within the synaptic vesicles. The amino acids glycine and glutamic acid are normal constituents of proteins and are present in abundance in the axons. These are also stored in synaptic vesicles. Each electrical impulse that arrives at the presynaptic side of a synapse will cause only a small minority of the synaptic vesicles to fuse with the plasma membrane and discharge their contents. The remaining synaptic vesicles remain, waiting for subsequent electrical impulses. At the same time, neurotransmitter synthesis continues, as does their storage in synaptic vesicles. This tends to restore the full complement of amine neurotransmitters at the axon terminal. 

Glutamic acid is removed by a transporter molecule which brings it back through the presynaptic membrane unto the neuron. 

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