Similarity of A(3)-adenosine and swelling-activated Cl- channels in nonpigmented ciliary epithelial cells

Chloride release from nonpigmented ciliary epithelial (NPE) cells is a fina l step in forming aqueous humor, and adenosine stimulates Cl- transport by these cells. Whole cell patch clamping of cultured human NPE cells indicate d that the A(3)-selective agonist 1-deoxy-1-(6-[([3-iodophenyl] methyl) ami no]-9H-purin-9- yl)-N-methyl-beta-D-ribofuranuronamide (IB-MECA) stimulated currents (IIB-MECA) by similar to 90% at +80 mV. Partial replacement of ex ternal Cl- with aspartate reduced outward currents and shifted the reversal potential (V-rev) from -23 +/- 2 mV to -0.0 +/- 0.7 mV. Nitrate substituti on had little effect. Perfusion with the Cl- channel blockers 5-nitro-2-(3- phenylpropylamino) benzoic acid (NPPB) and niflumic acid inhibited the curr ents. Partial Cl- replacement with aspartate and NO3-, and perfusion with N PPB, had similar effects on the swelling-activated whole cell currents (I-S well). Partial cyclamate substitution for external Cl- inhibited inward and outward currents of both IIB-MECA and I-Swell. Both sets of currents also showed outward rectification and inactivation at large depolarizing potenti als. The results are consistent with the concept that A(3)-subtype adenosin e agonists and swelling activate a common population of Cl- channels.