A3adenosine receptors regulate Cl−channels of nonpigmented ciliary epithelial cells

Publisher Website
Google Scholar
Abstract
Adenosine stimulates Cl− channels of the nonpigmented (NPE) cells of the ciliary epithelium. We sought to identify the specific adenosine receptors mediating this action. Cl− channel activity in immortalized human (HCE) NPE cells was determined by monitoring cell volume in isotonic suspensions with the cationic ionophore gramicidin present. The A3-selective agonistN6-(3-iodobenzyl)-adenosine-5′-N-methyluronamide (IB-MECA) triggered shrinkage (apparentKd = 55 ± 10 nM). A3-selective antagonists blocked IB-MECA-triggered shrinkage, and A3-antagonists (MRS-1097, MRS-1191, and MRS-1523) also abolished shrinkage produced by 10 μM adenosine when all four known receptor subtypes are occupied. The A1-selective agonistN6-cyclopentyladenosine exerted a small effect at 100 nM but not at higher or lower concentrations. The A2A agonist CGS-21680 triggered shrinkage only at high concentration (3 μM), an effect blocked by MRS-1191. IB-MECA increased intracellular Ca2+ in HCE cells and also stimulated short-circuit current across rabbit ciliary epithelium. A3 message was detected in both HCE cells and rabbit ciliary processes using RT-PCR. We conclude that human HCE cells and rabbit ciliary processes possess A3 receptors and that adenosine can activate Cl− channels in NPE cells by stimulating these A3receptors.