Publications

• Flux coupling in a neuronal glutamate transporter.

  Zerangue N., Kavanaugh M.P.

  Synaptic transmission is commonly terminated by diffusion and reuptake of neurotransmitter from the synaptic cleft. Glutamate reuptake prevents neurotoxicity and sets the lower limit for the concentration of extracellular glutamate, so it is important to understand the thermodynamics of this proce ... >> More

  Synaptic transmission is commonly terminated by diffusion and reuptake of neurotransmitter from the synaptic cleft. Glutamate reuptake prevents neurotoxicity and sets the lower limit for the concentration of extracellular glutamate, so it is important to understand the thermodynamics of this process. Here we use voltage clamping with a pH-sensitive fluorescent dye to monitor electrical currents and pH changes associated with flux of glutamate mediated by the human neuronal glutamate transporter EAAT3. In contrast to a previous model, we find that three sodium ions and one proton are cotransported with each glutamate ion into the cell, while one potassium ion is transported out of the cell. This coupling can support a transmembrane glutamate concentration gradient ([Glu]in/[Glu]out) exceeding 10(6) under equilibrium conditions, and would allow the transporter to continue removing glutamate over a wide range of ionic conditions. << Less

  Nature 383:634-637(1996) [PubMed] [EuropePMC]

• Stoichiometry of the glial glutamate transporter GLT-1 expressed inducibly in a Chinese hamster ovary cell line selected for low endogenous Na+-dependent glutamate uptake.

  Levy L.M., Warr O., Attwell D.

  Glutamate transport across the plasma membrane of neurons and glia is powered by the transmembrane electrochemical gradients for sodium, potassium, and pH, but there is controversy over the number of Na+ cotransported with glutamate. The stoichiometry of glutamate transporters is important because ... >> More

  Glutamate transport across the plasma membrane of neurons and glia is powered by the transmembrane electrochemical gradients for sodium, potassium, and pH, but there is controversy over the number of Na+ cotransported with glutamate. The stoichiometry of glutamate transporters is important because it determines a lower limit to the extracellular glutamate concentration, [glu]o, in both normal and pathological conditions. We used whole-cell clamping to study the stoichiometry of the glial transporter GLT-1, the most abundant glutamate transporter in the brain, expressed under control of the Tet-On system in a Chinese hamster ovary (CHO) cell line selected for low endogenous glutamate transport. After the induction of GLT-1 expression with doxycycline, glutamate evoked a Na+-dependent inward current with the voltage dependence and pharmacology of GLT-1 and acidified the cell cytoplasm. Raising [K+]o around cells clamped with electrodes containing sodium and glutamate evoked an outward reversed uptake current. These responses were reduced by the specific GLT-1 blocker dihydrokainate (DHK). DHK evoked an outward current with NO3-, but not with Cl-, as the main intracellular anion, suggesting that the anion conductance of the transporter is active even without external glutamate but generates little current in the absence of highly permeable anions like NO3-. Measuring the reversal potential of the transporter current in various ionic conditions suggested that the transport of one glutamate anion is coupled to the cotransport of three Na+ and one H+ and to the countertransport of one K+. This suggests that in ischemia, when [K+]o rises to 60 mM, the reversal of glutamate transporters will raise [glu]o to >50 microM. << Less

  J Neurosci 18:9620-9628(1998) [PubMed] [EuropePMC]