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Adenosine regulation of alveolar fluid clearance

Factor, Phillip, Mutlu, Göskhan M., Chen, Lan, Mohameed, Jameel, Akhmedov, Alexander T., Meng, Fan Jing, Jilling, Tamas, Lewis, Erin Rachel, Johnson, Meshell D., Xu, Anna, Kass, Daniel, Martino, Janice M., Bellmeyer, Amy, Albazi, John S., Emala, Charles, Lee, H.T., Dobbs, Leland G., Matalon, Sadis
Proceedings of the National Academy of Sciences of the United States of America 2007 v.104 no.10 pp. 4083-4088
absorption, adenosine, adenylate cyclase, chlorides, cyclic AMP, edema, epithelial cells, epithelium, ligands, lungs, mice, purinergic receptors, rats, sodium
Adenosine is a purine nucleoside that regulates cell function through G protein-coupled receptors that activate or inhibit adenylyl cyclase. Based on the understanding that cAMP regulates alveolar epithelial active Na⁺ transport, we hypothesized that adenosine and its receptors have the potential to regulate alveolar ion transport and airspace fluid content. Herein, we report that type 1 (A₁R), 2a (A₂aR), 2b (A₂bR), and 3 (A₃R) adenosine receptors are present in rat and mouse lungs and alveolar type 1 and 2 epithelial cells (AT1 and AT2). Rat AT2 cells generated and produced cAMP in response to adenosine, and micromolar concentrations of adenosine were measured in bronchoalveolar lavage fluid from mice. Ussing chamber studies of rat AT2 cells indicated that adenosine affects ion transport through engagement of A₁R, A₂aR, and/or A₃R through a mechanism that increases CFTR and amiloride-sensitive channel function. Intratracheal instillation of low concentrations of adenosine (=10⁻⁶M) reduced AFC in mice and rats via an A₁R-dependent pathway. Instillation of a CFTR inhibitor (CFTRinh₋₁₇₂) attenuated adenosine-mediated down-regulation of AFC, suggesting that adenosine causes Cl⁻ efflux by means of CFTR. These studies report a role for adenosine in regulation of alveolar ion transport and fluid clearance. These findings suggest that physiologic concentrations of adenosine allow the alveolar epithelium to counterbalance active Na⁺ absorption with Cl⁻ efflux through engagement of the A₁R and raise the possibility that adenosine receptor ligands can be used to treat pulmonary edema.