Noise analysis of the glutamate-activated current in photoreceptors

Hans P Larsson, S. A. Picaud, F. S. Werblin, H. Lecar

Research output: Contribution to journalArticle

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Abstract

The glutamate-activated current in photoreceptors has been attributed both to a sodium/glutamate transporter and to a glutamate-activated chloride channel. We have further studied the glutamate-activated current in single, isolated photoreceptors from the tiger salamander using noise analysis on whole-cell patch-clamp recordings. In cones, the current is generated by chloride channels with a single-channel conductance of 0.7 pS and an open lifetime of 2.4 ms. The number of channels per cell is in the range of 10,000- 20,000. Activation of the channels requires the presence of both glutamate and sodium. The single-channel conductance and the open lifetime of the channel are independent of the external concentration of glutamate and sodium. External glutamate and sodium affect only the opening rate of the channels. D,L-Threo-3-hydroxyaspartate (THA), a glutamate-transport blocker, is shown to be a partial agonist for the channel. The single-channel conductance is the same regardless of whether glutamate or THA is the ligand, but the open lifetime of the channel is only 0.8 ms with THA as ligand. The glutamate-activated current in rods has a similar single-channel conductance (0.74 pS) and open lifetime (3 ms). We propose a kinetic model, consistent with these results, to explain how a transporter can simultaneously act both as a sodium/glutamate-gated chloride channel and a glutamate/sodium cotransporter.

Original languageEnglish
Pages (from-to)733-742
Number of pages10
JournalBiophysical Journal
Volume70
Issue number2 I
StatePublished - Feb 1 1996
Externally publishedYes

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Noise
Glutamic Acid
Sodium Glutamate
Glutamate Plasma Membrane Transport Proteins
Chloride Channels
Ambystoma
Ligands

ASJC Scopus subject areas

  • Biophysics

Cite this

Larsson, H. P., Picaud, S. A., Werblin, F. S., & Lecar, H. (1996). Noise analysis of the glutamate-activated current in photoreceptors. Biophysical Journal, 70(2 I), 733-742.

Noise analysis of the glutamate-activated current in photoreceptors. / Larsson, Hans P; Picaud, S. A.; Werblin, F. S.; Lecar, H.

In: Biophysical Journal, Vol. 70, No. 2 I, 01.02.1996, p. 733-742.

Research output: Contribution to journalArticle

Larsson, HP, Picaud, SA, Werblin, FS & Lecar, H 1996, 'Noise analysis of the glutamate-activated current in photoreceptors', Biophysical Journal, vol. 70, no. 2 I, pp. 733-742.
Larsson HP, Picaud SA, Werblin FS, Lecar H. Noise analysis of the glutamate-activated current in photoreceptors. Biophysical Journal. 1996 Feb 1;70(2 I):733-742.
Larsson, Hans P ; Picaud, S. A. ; Werblin, F. S. ; Lecar, H. / Noise analysis of the glutamate-activated current in photoreceptors. In: Biophysical Journal. 1996 ; Vol. 70, No. 2 I. pp. 733-742.
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