Glutamate-gated chloride channel with glutamate-transporter-like properties in cone photoreceptors of the tiger salamander.
1. Using the patch-clamp technique, we investigated whether the glutamate-elicited current in mechanically isolated cone photoreceptors from the salamander retina is generated by a Cl- channel or a glutamate transporter. 2. The current reversed near the equilibrium potential for Cl-, was decreased by three Cl- channel blockers, 5-nitro-2-(3-phenyl-propylamino) benzoic acid, 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and diphenylamine 2,2'-dicarboxylic acid, and was eliminated when gluconate was substituted for both internal and external Cl-, features consistent with the current being mediated by a Cl- channel. 3. The single-channel conductance of the Cl- channel was estimated by noise analysis of the glutamate-elicited current fluctuations to be 0.7 pS with an open time of 2 ms. 4. The magnitude of the current was dependent on both internal and external Na+ and K+, features consistent with the current being related to the activation of a glutamate transporter. Yet changes in their concentrations did not affect the reversal potential of the current. 5. Taken together with earlier reports on this current showing that it has a glutamate-transporter-like pharmacology, our results suggest that the glutamate-elicited current is carried by a Cl- channel but gated by a glutamate receptor whose pharmacology and ionic requirement resemble those previously described for glutamate transporters.
Picaud
S A
SA
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
Larsson
H P
HP
Grant
G B
GB
Lecar
H
H
Werblin
F S
FS
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism*; D002712:Chlorides / Q000502:physiology; D004553:Electric Conductivity; D018698:Glutamic Acid / Q000494:pharmacology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007608:Kainic Acid / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology / Q000502:physiology; D017470:Receptors, Glutamate / Q000378:metabolism; D017949:Retinal Cone Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology / Q000502:physiology; D014562:Caudata / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D018118:Chloride Channels; D002712:Chlorides; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D012964:Sodium; D011188:Potassium; D007608:Kainic Acid