A₁ and A₂ adenosine receptors in rabbit cortical collecting tubule cells. Modulation of hormone-stimulated cAMP

Adenosine analogs were used to investigate the cellular mechanisms by which adenosine may alter renal tubular function. Cultured rabbit cortical collecting tubule (RCCT) cells, isolated by immunodissection, were treated with 5'-N-ethylcarboxamideadenosine (NECA), N⁶-cyclohexyladenosine (CHA), and R-N⁶-phenylisopropyladenosine (PIA). All three analogs produced both dose-dependent inhibition and stimulation of RCCT cell cyclic AMP (cAMP) production. Stimulation of cAMP accumulation occurred at analog concentrations of 0.1 μM to 100 μM with the rank order of potency NECA > PIA > CHA. Inhibition occurred at concentrations of 1 nM to 1 μM with the rank order of potency CHA > PIA > NECA. These effects on cAMP production were inhibited by 1,3-diethyl-8-phenylxanthine and isobutylmethylxanthine. CHA (50 nM) blunted AVP- and isoproterenol-stimulated cAMP accumulation. This modulation of hormone-induced cAMP production was abolished by pretreatment of RCCT cells with pertussis toxin. Prostaglandin E₂ production was unaffected by 0.1 mM CHA. These findings indicate the presence of both inhibitory (A₁) and stimulatory (A₂) receptors for adenosine in RCCT cells. Moreover, occupancy of the A₁ receptor causes inhibition of both basal and hormone-stimulated cAMP formation through an action on the inhibitory guanine nucleotide-binding regulatory component, N(i), of the adenylate cyclase system.