Journal of Neurochemistry · 1976 · 96 citations · 33 references
Synaptic TransmissionNeurotransmitterNeurotransmissionExperimental PharmacologySynaptic SignalingSocial SciencesNeurologyNeurochemistryMolecular NeuroscienceSodium HomeostasisNeuropharmacologyCerebral Blood FlowNervous SystemPharmacologyInhibitory NeurotransmittersSynaptic PlasticityAmino AcidNeurophysiologyCellular NeuroscienceL ‐Glutamate UptakePhysiologyBrain ElectrophysiologyNeuroscienceCentral Nervous SystemMolecular NeurobiologyMedicineBrain Cortex Slices
Abstract— 1. Whereas exogenous l ‐glutamate enters rat brain cortex slices incubated in a glucose‐physiological saline medium by both low affinity (K m = 0.7 m m ) and high affinity (K m = 27−30 μM) processes, the uptake of d ‐glutamate occurs only by a low affinity (K m = 2m m ) system. 2. d ‐glutamate appears to release l ‐glutamate from incubated rat brain cortex slices only to a very small extent, whether the tissue l ‐glutamate is of endogenous or exogenous origin. 3. Competitive inhibition takes place between l ‐ and d ‐glutamates at the low affinity carrier. This indicates that a common carrier exists for l ‐ and d ‐glutamates for the low affinity uptake process. 4. Apparently non‐competitive inhibition by d ‐glutamate of l ‐glutamate uptake occurs at the high affinity carrier, but the affinity of d ‐glutamate for this carrier is about 0.4% of that of l ‐glutamate. 5. Both d ‐, and l ‐glutamate exchange freely with labelled d ‐glutamate taken up by preliminary incubation of the brain slices with this amino acid. Whereas l ‐glutamate exchanges freely with labelled l ‐glutamate taken up by preliminary incubation, d ‐glutamate shows little or no exchange. 6. The uptake of labelled d ‐glutamate by exchange diffusion into brain slices previously loaded with unlabelled d ‐glutamate proceeds by a low affinity system. Therefore, the process of exchange diffusion does not necessarily involve a high affinity uptake component. 7. Whereas ouabain suppresses both high and low affinity concentrative uptakes of l ‐ and d ‐glutamate it has little apparent effect on the exchange diffusion process. 8. Sensitivity to tetrodotoxin of evoked release of l ‐ and d ‐glutamates, taken up by brain slices by preliminary incubation with these amino acids, indicates that the major proportion of the uptake of exogenous l ‐ or d ‐glutamate proceeds into non‐neuronal structures (presumably the glia). 9. At 0°C non‐carrier mediated (passive) diffusion of labelled d ‐ and l ‐glutamate takes place in brain slices.
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