CHARACTERIZATION OF CYCLIC-AMP EFFLUX FROM SWINE ADIPOCYTES IN-VITRO

Objective: A variety of cell types transport cyclic AMP (cAMP) to the extracellular fluid; the purpose of this study was to determine if and how this process occurs in adipocytes. Research Methods and Procedure s: Adipocytes were isolated from 3-month-old swine and incubated with stimulators of adenylate cyclase for 2 to 120 minutes to promote cAMP synthesis and efflux, Efflux was characterized in the presence of agen ts that inhibit ATP production, anion transport, intracellular cAMP me tabolism, and extracellular cAMP metabolism. Extracellular cAMP was me asured by enzyme immunoassay, then corrected for cell lysis by measuri ng lactate dehydrogenase release. Results: cAMP efflux averaged 24.7 f mol/min/cm(2) adipocyte surface area, was linear for 2 hours, and was proportional to adipocyte surface area (r=0.94, p<0.05). Efflux was re duced by similar to 35% in cells incubated with 1 mu M antimycin, an i nhibitor of ATP synthesis (p<0.05), and by similar to 55% in cells inc ubated with 2 mM probenecid, an anion-specific transport blocker (p<0. 05). Extracellular cAMP levels more than doubled by the addition of 1 mu M 1,3-dipropyl-8-p-sulfophenylxanthine, a purported inhibitor of ex tracellular phosphodiesterase. Discussion: Our data demonstrate that c AMP is transported from swine adipocytes by an energy-dependent anion transporter and can be metabolized extracellularly. Future studies wil l evaluate extracellular cAMP as a potential source of extracellular a denosine, a potent inhibitor of adipocyte lipolysis.