A chloride conductance in VGLUT1 underlies maximal glutamate loading into synaptic vesicles.
Uptake of glutamate into synaptic vesicles is mediated by vesicular glutamate transporters (VGLUTs). Although glutamate uptake has been shown to depend critically on Cl(-), the precise contribution of this ion to the transport process is unclear. We found that VGLUT1, and not ClC-3 as proposed previously, represents the major Cl(-) permeation pathway in synaptic vesicles. Using reconstituted VGLUT1, we found that the biphasic dependence of glutamate transport on extravesicular Cl(-) is a result of the permeation of this anion through VGLUT1 itself. Moreover, we observed that high luminal Cl(-) concentrations markedly enhanced loading of glutamate by facilitation of membrane potential-driven uptake and discovered a hitherto unrecognized transport mode of VGLUT1. Because a steep Cl(-) gradient across the synaptic vesicle membrane exists in endocytosed synaptic vesicles, our results imply that the transport velocity and the final glutamate content are highly influenced, if not determined, by the extracellular Cl(-) concentration.
Schenck
Stephan
S
Center for Brain Integration Research, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
Wojcik
Sonja M
SM
Brose
Nils
N
Takamori
Shigeo
S
D000143:Acids / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000166:cytology; D018118:Chloride Channels / Q000235:genetics / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009474:Neurons / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism*; D050598:Vesicular Glutamate Transport Protein 1 / Q000235:genetics / Q000378:metabolism*
D000143:Acids; D018118:Chloride Channels; D002712:Chlorides; C115376:ClC-3 channel; D008081:Liposomes; C493465:Slc17a7 protein, mouse; D050598:Vesicular Glutamate Transport Protein 1; D018698:Glutamic Acid