Adenosine inhibits arginine vasopressin-stimulated chloride secretion in a mouse imcd cell line (mimcd-k2). Moyer, Bryan D., David E. McCoy, Brian Lee, Neil Kizer, and Bruce A. Stanton. Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire USA 03755
APStracts 2:0111F, 1995.
Previously we demonstrated that a mouse inner medullary collecting duct cell line (mIMCD-K2) secretes chloride (Cl-) by an electrogenic mechanism via cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels (15,16,32). The objective of the present study was to determine if adenosine, and adenosine A1 receptors (A1AR) specifically, regulate electrogenic Cl- secretion (IClsc) in mIMCD-K2 cells. Neither N6-cyclohexyladenosine (CHA), a specific A1AR agonist, nor 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a specific A1AR antagonist, altered basal, unstimulated IClsc in monolayers of mIMCD -K2 cells mounted in Ussing-type chambers. In contrast, DPCPX increased arginine vasopressin (AVP)-stimulated IClsc; an effect that was reversed by CHA. Adenosine deaminase (ADA), which oxidatively deaminates adenosine to inosine, increased AVP-stimulated IClsc. CHA reversed the stimulatory effect of ADA on AVP-stimulated IClsc. These results suggest that adenosine, via A1AR, inhibits AVP-stimulated IClsc. To identify the source(s) of extracellular adenosine we examined 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 IClsc. Both compounds increased AVP-stimulated IClsc. CHA reversed the stimulatory effect of dipyridamole and AOPCP on IClsc. Neither ADA nor CHA had an effect on 8-(4-chlorophenylthio)-cyclic adenosine monophosphate (CPT-cAMP)-stimulated IClsc. Moreover, U73122, an inhibitor of phospholipase C, failed to attenuate the increase in AVP-stimulated IClsc elicited by dipyridamole and AOPCP or the decrease in AVP-stimulated IClsc elicited by CHA. We conclude that adenosine, released by a nucleoside transporter and formed extracellularly by the breakdown of adenosine 5'-monophosphate (5' -AMP), binds to A1AR and decreases AVP-stimulated IClsc in mIMCD-K2 cells by reducing intracellular cAMP levels. 

Received 6 April 1995; accepted in final form 9 June 1995.
APS Manuscript Number F118-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.