Electrogenic Hyperpolarization-Elicited Chloride Transporter Current in Blue Cones of Zebrafish Retinal Slices

Voltage-activated currents in blue cones of the retinal slice of zebrafish were characterized using whole cell recording techniques. Depolarizing-elicited currents were recorded: an outward tetraethylammonium (TEA)-sensitive K+ current (IKx), an outward Ca(2+)-activated Cl- current (ICl(Ca)), from which we inferred an inward Ca2+ current (ICa) as well as a hyperpolarizing-elicited nonselective inward cation current (Ih). In addition, hyperpolarizing steps elicited an outward current (Iout-h) in about one-third of the blue cones. Iout-h seems to be carried by inward transported Cl- because it was abolished by equimolar substitution of bath Cl- with acetate; equimolar substitution of Na+ with choline or TEA had no effect; it was not affected by Cl- channel blockers, anthracene-9-carboxylic acid, 4,4'-diisothiocyanostilbene-2.2'-disulfonic acid, N-phenylanthranilic acid (DPC), niflumic acid, and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but was suppressed by Cl- transporter blockers acetalzolamide, bumetanide, N-ethylmaleimide, furosemide, and vanadate, and no reversal potential was found. In addition, this current was suppressed by ouabains but unrelated to their Na(+)-K(+)-ATPase inhibitory effect, was not suppressed by Co2+ or nifedipine, was not affected by the gap junction decoupler, 2-octanol, was increased by bath application of Cs+, presumably due to suppression of Ih, which was masked by Iout-h, and was suppressed by intensive light. Similar current also was found in the short cones and double cones. As Iout-h operates over the same voltage range, and with similar magnitude and time course as Ih, we suggest that Iout-h contributes to the modulation of the photoresponse of cones.