Abstract
Intracellular and patch-clamp recordings have been used to characterize GABA-activated channels in axonless horizontal cells (ALHC) of the rabbit retina. In our intracellular recordings on an everted eyecup preparation, GABA depolarized the horizontal cells (HC), diminished their light response amplitude and slowed the response rise time. Glycine showed similar effects on the HC ligth responses. In our whole cell patch-clamp recordings on dissociated ALHC, all HCs responded to 3 μM GABA but none to glycine, even at 100 μ.M. Dose-response relationship for GABA gave EC 50 values around 10 μM and Hill slopes of 1.3. Whole-cell current-voltage ( I–V) relationships of GABA-activated currents reversed close to the predicted Cl − equilibrium potential. Partial replacement of intracellular CI- with isothetionate shifted the GABA reversal potential to a more negative value. Muscimol (30 μM), a GABAA agonist mimicked the effect of GABA, but baclofen (30 μM), a GABA b agonist and cis-aminocaprionic acid (30 μM), a GABA agonist did not elicit any effect on ALHC. Responses to GABA were blocked by the GABA A receptor antagonist bicuculline (10) μM) and picrotoxin (100 μM). According to our results, we conclude that ALHC express GABA receptors coupled to ion channels, and they correspond to GABA A receptor subtypes.
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