Dynamics of forward and reverse transport by the glial glycine transporter, glyt1b.
Glycine is a coagonist at the N-methyl-D-aspartate receptor. Changes in extracellular glycine concentration may modulate N-methyl-D-aspartate receptor function and excitatory synaptic transmission. The GLYT1 glycine transporter is present in glia surrounding excitatory synapses, and plays a key role in regulating extracellular glycine concentration. We investigated the kinetic and other biophysical properties of GLYT1b, stably expressed in CHO cells, using whole-cell patch-clamp techniques. Application of glycine produced an inward current, which decayed within a few seconds to a steady-state level. When glycine was removed, a transient outward current was observed, consistent with reverse transport of accumulated glycine. The outward current was enhanced by elevating intracellular or lowering extracellular [Na(+)], and was modulated by changes in extracellular [glycine] and time of glycine application. We developed a model of GLYT1b function, which accurately describes the time course of the transporter current under a range of experimental conditions. The model predicts that glial uptake of glycine will decay toward zero during a sustained period of elevated glycine concentration. This property of GLYT1b may permit spillover from glycinergic terminals to nearby excitatory terminals during a prolonged burst of inhibitory activity, and reverse transport may extend the period of elevated glycine concentration beyond the end of the inhibitory burst.
Aubrey
Karin R
KR
Department of Pharmacology, Institute for Biomedical Research, University of Sydney, NSW 2006, Australia. aubrey@biologie.ens.fr
Vandenberg
Robert J
RJ
Clements
John D
JD
D000818:Animals; D001692:Biological Transport; D001703:Biophysics / Q000379:methods*; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism; D005998:Glycine / Q000737:chemistry*; D050487:Glycine Plasma Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology; D007700:Kinetics; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry; D012964:Sodium / Q000737:chemistry; D013569:Synapses / Q000502:physiology; D013997:Time Factors
D050485:GABA Plasma Membrane Transport Proteins; D050487:Glycine Plasma Membrane Transport Proteins; D016194:Receptors, N-Methyl-D-Aspartate; C493266:Slc6a9 protein, rat; D012964:Sodium; D005998:Glycine