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

Abstract

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 ϩ 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

Inhibition of glutamate uptake by a polypeptide toxin (phoneutriatoxin 3-4) from the spider Phoneutria nigriventer

“…Figure 2(C) shows that Tx3-4 (8 nM) was able to inhibit glutamate uptake in GPVs by only 9.5 % after 30 min of preincubation with the toxin. Dihydrokainate was able to decrease uptake by 70 % under the same conditions, showing that the uptake was due to glial glutamate transporters [21,26].…”

Inflammation, Glutamate, and Glia: A Trio of Trouble in Mood Disorders

“…EAATs can transport glutamate against a 10 000-fold difference in concentration gradient between intra-and extracellular compartments (Milton et al, 1997). EAATs accomplish this seemingly impossible task by pairing glutamate intake with inward transfer of three Na+ ions and one H+ ion, and outward transfer of one K+ ion from the cell, resulting in a net inward movement of positive charge (Levy et al, 1998;Zerangue and Kavanaugh, 1996).…”

Reversed Actrocytic GLT-1 during Ischemia is Crucial to Excitotoxic Death of Neurons, but Contributes to the Survival of Astrocytes themselves

“…The uptake of glutamate by sodium-dependent glutamate transporters such as astrocytic GLT-1 is driven by the co-transport of three sodium ions and one proton with each glutamate ion into the cell, while one potassium ion is transported out of the cell (5)(6)(7). During ischemia, the activity of Na + ,K + -ATPase is markedly suppressed, resulting in the accumulation of intracellular sodium ions (8).…”