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 final step in forming aqueous humor, and adenosine stimulates Cl− transport by these cells. Whole cell patch clamping of cultured human NPE cells indicated that the A3-selective agonist 1-deoxy-1-(6-[([3-iodophenyl]methyl)amino]-9H-purin-9-yl)- N-methyl-β-d-ribofuranuronamide (IB-MECA) stimulated currents ( I IB-MECA) by ∼90% at +80 mV. Partial replacement of external Cl−with aspartate reduced outward currents and shifted the reversal potential ( V rev) from −23 ± 2 mV to −0.0 ± 0.7 mV. Nitrate substitution had little effect. Perfusion with the Cl− channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and niflumic acid inhibited the currents. Partial Cl− replacement with aspartate and NO3 −, and perfusion with NPPB, had similar effects on the swelling-activated whole cell currents ( I Swell). Partial cyclamate substitution for external Cl− inhibited inward and outward currents of both I IB-MECA and I Swell. Both sets of currents also showed outward rectification and inactivation at large depolarizing potentials. The results are consistent with the concept that A3-subtype adenosine agonists and swelling activate a common population of Cl− channels.