ELECTROGENIC HYPERPOLARIZATION-ELICITED CHLORIDE TRANSPORTER CURRENT IN BLUE CONES OF ZEBRAFISH RETINAL SLICES

Voltage-activated currents in blue cones of the retinal slice of zebra fish were characterized using whole cell recording techniques. Depolar izing-elicited currents were recorded: an outward tetraethylammonium ( TEA)-sensitive K+ current (I-Kx), an outward Ca2+-activated Cl- curren t (I-Cl(Ca)), from which we inferred an inward Ca2+ current (I-Ca) as well as a hyperpolarizing-elicited nonselective inward cation current (I-h). In addition, hyperpolarizing steps elicited an outward current (Iout-h) in about one-third of the blue cones. Iout-h seems to be carr ied by inward transported Cl- because it was abolished by equimolar su bstitution of bath Cl- with acetate; equimolar substitution of Na+ wit h choline or TEA had no effect; it was not affected by Cl- channel blo ckers, anthracene-9-carboxylic acid, 4,4'-diisothiocyano-stilbene-2,2' -disulfonic acid, N-phenylanthranilic acid (DPC), niflumic acid, and - acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but was suppres sed by Cl- transporter blockers acetalzolamide, bumetanide, N-ethylmal eimide, 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 suppressi on of I-h, which was masked by Iout-h, and was suppressed by intense l ight. Similar current also was found in the short cones and double con es. As Iout-h operates over the same voltage range, and with similar m agnitude and time course as I-h, we suggest that Iout-h contributes to the modulation of the photoresponse of cones.