Adenosine induces cyclic-AMP formation and inhibits endothelin-1 production/secretion in guinea-pig tracheal epithelial cells through A2B adenosine receptors

1 The adenosine receptor subtype mediating adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation and the effect of its activation on endothelin-l (ET-l) secretion were studied in primary cultures of tracheal epithelial cells. 2 Adenosine analogues showed the following rank order of potency (pD(2) value) and intrinsic activity on the generation of cyclic AMP by tracheal epithelial cells: 5'-N-ethylcarboxyamidoadenosine (NECA, A(1)/A(2A)/A(2B), pD(2): 5.44 +/- 0.16) > adenosine (ADO, non selective, pD(2): 4.99 +/- 0.09; 71 +/- 9% of NECA response) greater than or equal to 2-Cl-adenosine (2CADO, non selective, pD(2): 4.72 +/- 0.14; 65 +/- 9% of NECA response) > > > CGS21680 (A(2A); inactive at up to 100 mu M). 3 Cyclic AMP formation stimulated by NECA in guinea-pig tracheal epithelial cells was inhibited by adenosine receptor antagonist with the following order of apparent affinity (pA(2) value): Xanthine amine congeners (XAC, A(2A)/A(2B), 7.89 +/- 0.22) > CGS15943 (A(2A)/A(2B), 7.24 +/- 0.26) > ZM241385 (A(2A) 6.69 +/- 0.14) > DPCPX (A(1), 6.51 +/- 0.14) > 3n-propylxanthine (weak A(2B), 4.30 +/- 0.10). This rank order of potency is typical for A(2B)-adenosine receptor. 4 Adenosine decreased basal and LPS-stimulated irET production in a concentration-dependent manner. Moreover, NECA but not CGS21680 inhibited LPS-induced irET production. 5 The inhibitory effect of NECA on LPS-induced irET production was reversed by XAC (pA(2) = 8.84 +/- 0.12) and DPCPX (pA(2) = 8.10 +/- 0.22). 6 These results suggested that adenosine increased cyclic AMP formation and inhibited irET production/secretion by guinea-pig tracheal epithelial cells through the activation of a functional adenosine receptor that is most likely the A(2B) subtype. This adenosine receptor may be involved in the regulation of the level of ET-I production/secretion by guinea-pig tracheal epithelial cells in physiological as well as in pathophysiological conditions.