Adenosine inhibits arginine vasopressin-stimulated chloride secretion in a mouse IMCD cell line (mIMCD-K2)

Previously, we demonstrated that a mouse inner medullary collecting duct cell line (mIMCD-K2) secretes Cl- by an electrogenic mechanism via cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels [N. L. Kizer, B. Lewis, and B. A. Stanton. An. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F347-F355, 1995; N. L. Kiter, D. Vandorpe, B. Lewis, B. Bunting, J. Russell, and B. A. Stanton. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F854-F861, 1995; D. Vandorpe, N. Kiter, F. Ciampolillo-Bates, B. Moyer, K. Karlson, W. B. Guggino, and B. A. Stanton. Am. J. Physiol. 269 (Cell Physiol. 38): C683-C689, 1995]. The objective of the present study was to determine whether adenosine, and adenosine Al receptors (A(1)AR) specifically, regulate electrogenic Cl- secretion (I-sc(Cl)) in mIMCD-K2 cells. Neither N-6-cyclohexyladenosine (CHA), a specific A,AR agonist, nor 8-cyclopentyl- 1,3-dipropylxanthine (DPCPX), a specific A(1)AR antagonist, altered basal, unstimulated I-sc(Cl) in monolayers of mIMCD-K2 cells mounted in Ussing-type chambers. In contrast, DPCPX increased arginine vasopressin (AVP)-stimulated I-sc(Cl), an effect that was reversed by CHA. Adenosine deaminase (ADA), which oxidatively deaminates adenosine to inosine, increased AVP-stimulated I-sc(Cl). CHA reversed the stimulatory effect of ADA on AVP-stimulated I-sc(Cl). These results suggest that adenosine, via A(1)AR, inhibits AVP-stimulated I-sc(Cl). To identify the source(s) of extracellular adenosine, we exam ined the effects of dipyridamole, an inhibitor of nucleoside transport, and alpha,beta-methyleneadenosine 5'-diphosphate (AOPCP), an inhibitor of ecto-5'-nucleotidase, on AVP-stimulated I-sc(Cl). Both compounds increased AVP-stimulated I-sc(Cl). CHA reversed the stimulatory effect of dipyridamole and AOPCP on I-sc(Cl). Neither ADA nor CHA had an effect on 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPT-cAMP)-stimulated I-sc(Cl). Moreover, U-73122, an inhibitor of phospholipase C, failed to attenuate the increase in AVP-stimulated I-sc(Cl) elicited by dipyridamole and AOPCP or the decrease in AVP-stimulated I-sc(Cl) elicited by CHA. We conclude that adenosine, released by a nucleoside transporter and formed extracellularly by the breakdown of AMP, binds to A(1)AR, and decreases AVP-stimulated I-sc(Cl) in mIMCD-K2 cells by reducing intracellular cAMP levels.