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Substrate turnover by transporters curtails synaptic glutamate transients
1Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, USA. menneris@psychiatry.wustl.edu
Summary
Inhibitors of glutamate transport prolong synaptic currents by affecting substrate translocation, not ambient glutamate levels. This finding clarifies the mechanism behind prolonged synaptic currents at excitatory synapses.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Glutamate transporter inhibitors prolong synaptic currents, but the underlying mechanism remains unclear.
- Potential mechanisms include direct interference with transporter function, altered glutamate binding, or increased ambient glutamate.
- Understanding these mechanisms is crucial for interpreting synaptic transmission and developing therapeutic strategies.
Purpose of the Study:
- To elucidate the precise mechanism by which glutamate transport inhibitors prolong synaptic currents.
- To differentiate between the roles of substrate translocation and ambient glutamate accumulation in synaptic current prolongation.
- To investigate the impact of astrocyte membrane potential on glutamate transporter activity.
Main Methods:
- Manipulating astrocyte membrane potential to assess its effect on synaptic currents and transporter kinetics.
- Utilizing excised membrane patches to study transporter currents and glutamate binding.
- Employing transporter substrates and non-substrate inhibitors to investigate ambient glutamate dynamics.
- Administering exogenous glutamate to mimic accumulation effects.
Main Results:
- Reversing astrocyte membrane potential prolonged synaptic currents without altering transporter affinity or kinetics.
- Positive membrane potentials did not affect glutamate analog binding or transporter availability.
- Elevated ambient glutamate from transporter substrates did not fully explain synaptic current prolongations.
- Exogenous glutamate failed to replicate the effects of substrate inhibitors on synaptic currents.
Conclusions:
- Substrate translocation by glutamate transporters plays a critical role in determining the duration of glutamate concentration transients at excitatory synapses.
- Ambient glutamate accumulation is not the primary driver of synaptic current prolongation caused by transporter inhibitors.
- These findings highlight the importance of transporter dynamics in regulating synaptic signaling.