Adenosine inhibits the basolateral Cl^- ClC-K2/b channel in collecting duct intercalated cells

Adenosine plays an important role in various aspects of kidney physiology, but the specific targets and mechanisms of actions are not completely understood. The collecting duct has the highest expression of adenosine receptors, particularly adenosine A₁ receptors (A₁Rs). Interstitial adenosine levels are greatly increased up to a micromolar range in response to dietary salt loading. We have previously shown that the basolateral membrane of principal cells has primarily K⁺ conductance mediated by K_ir4.1/5.1 channels to mediate K⁺ recycling and to set up a favorable driving force for Na⁺/K⁺ exchange (47). Intercalated cells express the Cl^- ClC-K2/b channel mediating transcellular Cl^- reabsorption. Using patch-clamp electrophysiology in freshly isolated mouse collecting ducts, we found that acute application of adenosine reversely inhibits ClC-K2/b open probability from 0.31 ± 0.04 to 0.17 ± 0.06 and to 0.10 ± 0.05 for 1 and 10 µM, respectively. In contrast, adenosine (10 µM) had no measureable effect on K_ir4.1/5.1 channel activity in principal cells. The inhibitory effect of adenosine on ClC-K2/b was abolished in the presence of the A₁R blocker 8-cyclopentyl-1,3-dipropylxanthine (10 µM). Consistently, application of the A₁R agonist N⁶-cyclohexyladenosine (1 µM) recapitulated the inhibitory action of adenosine on ClC-K2/b open probability. The effects of adenosine signaling in the collecting duct were independent from its purinergic counterpartner, ATP, having no measurable actions on ClC-K2/b and K_ir4.1/5.1. Overall, we demonstrated that adenosine selectively inhibits ClC-K2/b activity in intercalated cells by targeting A₁Rs. We propose that inhibition of transcellular Cl^- reabsorption in the collecting duct by adenosine would aid in augmenting NaCl excretion during high salt intake.