Extracellular glutamate: Functional compartments operate in different concentration ranges

Extra cellular glutamate of glial origin modulates glial and neuronal glutamate release and synaptic plasticity. Estimates of the tonic basal concentration of extra cellular glutamate range over three orders of magnitude (0.02-20 μM) depending on the technology employed to make the measurement. Based upon binding constants for glutamate receptors and transporters, this range of concentrations translates into distinct physiological and patho-physiological roles for extra cellular glutamate. Here we speculate that the difference in glutamate measurements can be explained if there is patterned membrane surface expression of glutamate release and transporter sites creating extra cellular sub compartments that vary in glutamate concentration and are preferentially sampled by different technologies.