Figure 2. Goldfish cones have GABA receptor-mediated Cl⁻ currents.

A, example of a whole-cell I–V relation of a cone in the presence or absence of GABA: Control (black trace), 200 μm GABA (red trace), Wash (blue trace). B, I–V relations of drug-induced (drug minus control) currents; 200 μm GABA induces a current reversing close to the calculated value for E_Cl−55 mV (red trace, n= 5). Application of 25 μm SKF89976-A, a GABA transporter blocker, leads to the closure of a current (black trace, n= 5), similar to the effect of 200 μm picrotoxin (PTX; green trace, n= 4). All currents reverse close to the estimated value of E_Cl. C, the GABA-induced (GABA minus control) I–V relations in conditions with a calculated E_Cl of −20 mV (black trace, n= 8) or −55 mV (red trace, n= 5). Changing E_Cl shifts the reversal potential of the currents near the values of the calculated E_Cl (−20 mV: −29.1 ± 3.5 mV; −55 mV: −48.8 ± 6.0 mV). D, example of cone current traces with or without light stimulation. To maximize the size of the Cl⁻ current, E_Cl was set to an estimated –20 mV and the cone was stepped to −102 mV. Next, HCs were hyperpolarized by a 3 s full-field light flash (red trace). This sequence did not elicit any current changes compared with cones kept in the dark following the same potential step (black trace) in all six cones tested.