P-2 PURINERGIC RECEPTOR AGONISTS ENHANCE CAMP PRODUCTION IN MADIN-DARBY CANINE KIDNEY EPITHELIAL-CELLS VIA AN AUTOCRINE PARACRINE MECHANISM

Mechanisms of cross-talk between different classes of signaling molecu les are inadequately understood, We have used clonal Madin-Darby canin e kidney (MDCK-D-1) epithelial cells as a model system to investigate the effects of extracellular nucleotides (e.g. ATP, UTP), which promot e increase in activity of several phospholipases, on cAMP production, In contrast to observations in some other cell systems, ATP and UTP, a cting via P-2 purinergic receptors, stimulated cAMP production in MDCK -D-1 cells, At maximally effective concentrations, ATP and UTP were no t additive with the beta-adrenergic receptor agonist isoproterenol, bu t were synergistic with forskolin in increasing cAMP production, indic ating that G(alpha s) is activated by these nucleotides, Additionally, we found that (a) nucleotide-induced increases in cAMP were blocked b y indomethacin, a cyclooxygenase inhibitor, (b) arachidonic acid incre ased cellular cAMP levels in an indomethacin sensitive fashion, and (c ) PGE(2), the major metabolite of arachidonic acid, stimulated cAMP fo rmation, Overall, our results suggest a mechanism by which extracellul ar nucleotides stimulate release of arachidonic acid which is metaboli zed to PGE(2) which, in turn, acts in an autocrine/paracrine fashion v ia prostaglandin receptors to activate G(alpha s) and increase cAMP, B ased on the ability of extracellular nucleotides to stimulate the form ation and release of prostaglandins in MDCK-D-1 epithelial and other c ells, we hypothesize that receptor-mediated prostaglandin release may be a general mechanism that regulates cAMP formation in many types of cells.