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Modulation of horizontal cell function by GABAA and GABAC receptors in dark- and light-adapted tiger salamander retina

Published online by Cambridge University Press:  01 September 1999

XIONG-LI YANG ,
FAN GAO  and
SAMUEL M. WU
XIONG-LI YANG
Affiliation:
Cullen Eye Institute, Baylor College of Medicine, Houston Present address: Shanghai Institute of Physiology, Chinese Academy of Sciences, 320 Yue Yang Rd., Shanghai 200031, China
FAN GAO
Affiliation:
Cullen Eye Institute, Baylor College of Medicine, Houston
SAMUEL M. WU
Affiliation:
Cullen Eye Institute, Baylor College of Medicine, Houston
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Abstract

The physiological function of GABA transporters and GABA receptors in retinal horizontal cells (HCs) under dark- and light-adapted conditions were studied by whole-cell voltage clamp and intracellular recording techniques in retinal slices and whole-mounted isolated retinas of the larval tiger salamander. Puff application of GABA in picrotoxin elicited a NO-711 (a potent GABA transporter blocker)-sensitive inward current that did not exhibit a reversal potential in the physiological range, consistent with the idea that these HCs contain electrogenic GABA transporters. Application of GABA in NO-711 elicited a chloride current in HCs; about half of the current was suppressed by bicuculline or I4AA (a GABAC receptor antagonist), and the remaining half was suppressed by bicuculline + I4AA or picrotoxin. In whole-mount retinas, NO-711, bicuculline, I4AA, or picrotoxin hyperpolarized the HCs and enhanced the light responses under dark-adapted conditions, and blocked the time-dependent recovery of HC membrane potential and light responses during background illumination. Based on the parallel conductance model, GABA released in darkness mediates a chloride conductance about three times greater than the leak conductance or the glutamate-gated cation conductance. About half of this chloride conductance is mediated by GABAA receptors, and the other half is mediated by GABAC receptors. These results suggest that GABA released from HCs through the NO-711-sensitive GABA transporters activates GABAA and GABAC receptors, resulting in chloride conductance increase which leads to a HC depolarization and reduction of the light response. Additionally, GABA transporters also mediate GABA release in background light that is responsible for the recovery of HC membrane potential and light responses.

Keywords

Retinal horizontal cellsGABAA receptorGABAC receptorGABA transporterLight adaptationChloride current
Type
Research Article
Information
Visual Neuroscience , Volume 16 , Issue 5 , September 1999 , pp. 967 - 979
Copyright
© 1999 Cambridge University Press

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