Retinal glial cell glutamate transporter is coupled to an anionic conductance.
Application of L-glutamate to retinal glial (Müller) cells results in an inwardly rectifying current due to the net influx of one positive charge per molecule of glutamate transported into the cell. However, at positive potentials an outward current can be elicited by glutamate. This outward current is eliminated by removal of external chloride ions. Substitution of external chloride with the anions thiocyanate, perchlorate, nitrate, and iodide, which are known to be more permeant at other chloride channels, results in a considerably larger glutamate-elicited outward current at positive potentials. The large outward current in external nitrate has the same ionic dependence, apparent affinity for L-glutamate, and pharmacology as the glutamate transporter previously reported to exist in these cells. Varying the concentration of external nitrate shifts the reversal potential in a manner consistent with a conductance permeable to nitrate. Together, these results suggest that the glutamate transporter in retinal glial cells is associated with an anionic conductance. This anionic conductance may be important for preventing a reduction in the rate of transport due the depolarization that would otherwise occur as a result of electrogenic glutamate uptake.
Eliasof
S
S
Vollum Institute, Oregon Health Sciences University, Portland 97201, USA.
Jahr
C E
CE
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000557:Ambystoma; D027322:Amino Acid Transport System X-AG; D000818:Animals; D000838:Anions; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D005942:Gluconates / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007454:Iodides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology*; D009566:Nitrates / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010472:Perchlorates / Q000494:pharmacology; D012160:Retina / Q000166:cytology*; D013861:Thiocyanates / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D000838:Anions; D018118:Chloride Channels; D002712:Chlorides; D005942:Gluconates; D007454:Iodides; D009566:Nitrates; D010472:Perchlorates; D013861:Thiocyanates; D018698:Glutamic Acid; C030691:gluconic acid