ROLE OF ADENOSINE ON GLUCAGON-INDUCED CAMP IN A HUMAN CORTICAL COLLECTING DUCT CELL-LINE

The hormonal responsiveness profile of the cortical collecting duct va ries from one species to another. To identify the hormones and agonist s that modulate the functions of this tubule segment in the human spec ies, we generated a cell line (HCD) immortalized by SV40 virus. The tu bular origin of this cell line was assessed by the expression of colle cting duct-specific antigens and the ability of vasopressin to increas e by nine-fold cAMP synthesis. Glucagon and adenosine stimulated cAMP synthesis, and atrial natriuretic peptide stimulated cGMP synthesis in a concentration-dependent manner. Bradykinin, adenosine and angiotens in increased intracellular calcium concentration ([Ca2+](i)). Because adenosine can regulate tubular functions, we examined its role on gluc agon-induced cAMP synthesis. Using adenosine analogs, we demonstrated that HCT cells both expressed adenosine type-2 (A2) receptors which st imulated cAMP production, and adenosine type 1 (A1) receptors linked t o [Ca2+](i) increase which inhibited glucagon-stimulated cAMP synthesi s. The inhibitory effect was abolished by pertussis toxin, and was nei ther due to [Ca2+](i) increase nor to protein kinase C activation, whi ch indicated that some A1 adenosine receptors were directly negatively coupled to adenylyl cyclase. These results suggest that adenosine can modify human cortical collecting duct functions in opposite ways acco rding to the adenosine receptor activated.