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The ionic stoichiometry of the GLAST glutamate transporter in salamander retinal glia
Author(s) -
Owe Simen Gylterud,
Marcaggi Païkan,
Attwell David
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.116830
Subject(s) - glutamate receptor , glutamate aspartate transporter , biophysics , transporter , cotransporter , extracellular , microdialysis , biochemistry , excitotoxicity , symporter , biology , chemistry , excitatory amino acid transporter , sodium , receptor , organic chemistry , gene
Maintaining a low extracellular glutamate concentration in the central nervous system is important for terminating synaptic transmission and preventing excitotoxic cell death. The stoichiometry of the most abundant glutamate transporter, GLT‐1, predicts that a very low glutamate concentration, ∼2 n m , should be reached in the absence of glutamate release, yet microdialysis measurements give a value of ∼1 μ m . If other glutamate transporters had a different stoichiometry, the predicted minimum glutamate concentration could be higher, for example if those transporters were driven by the cotransport of 2 Na + (rather than of 3 Na + as for GLT‐1). Here we investigated the ionic stoichiometry of the glutamate transporter GLAST, which is the major glutamate transporter expressed in the retina and cerebellum, is expressed in other adult brain areas at a lower level than GLT‐1, and is present throughout the brain early in development when expression of GLT‐1 is low. Glutamate transport by GLAST was found to be driven, as for GLT‐1, by the cotransport of 3 Na + and 1 H + and the counter‐transport of 1 K + , suggesting that the minimum extracellular glutamate concentration should be similar during development and in the adult brain. A less powerful accumulation of glutamate by GLAST than by GLT‐1 cannot be used to explain the high glutamate concentration measured by microdialysis.