Interaction between adenosine A 2B-receptors and alpha2-adrenoceptors on the modulation of noradrenaline release in the rat vas deferens: possible involvement of a group 2 adenylyl cyclase isoform.

In the prostatic portion of rat vas deferens, activation of adenosine A 2B-receptors, beta2-adrenoceptors, adenylyl cyclase or protein kinase A caused a facilitation of noradrenaline release. Blockade of alpha2-adrenoceptors with yohimbine (1 microM) attenuated the facilitation mediated by adenosine A 2B-receptors and by direct activation of adenylyl cyclase with forskolin but not that mediated by beta2-adrenoceptors or by direct activation of protein kinase A with 8-bromoadenosine-3',5'-cyclicAMP. The adenosine A 2B- and the beta2-adrenoceptor-mediated facilitation was prevented by the adenylyl cyclase inhibitors, 2',5'-dideoxy-adenosine (3 microM) and 9-cyclopentyladenine (100 microM), at concentrations that also attenuated the release enhancing effect of forskolin, but were not changed by the phospholipase C inhibitor 1-[6-[((17beta)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione (U-73122, 1 microM). Facilitation of noradrenaline release mediated by adenosine A 2B-receptors was also attenuated by activation of protein kinase C with the phorbol ester 12-myristate 13-acetate (1 microM) and by inhibition of Gbetagamma subunits with an anti-betagamma peptide; facilitation mediated by beta2-adrenoceptors was mainly attenuated by the calmodulin inhibitor calmidazolium (10 microM) and by the calmodulin kinase II inhibitor (N-[2-[N-(4-chlorocinnamyl)-N-methylaminomethyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzene-sulfonamide phosphate (KN-93, 5 microM). The results suggest that adenosine A 2B- but not beta2-adrenoceptor-mediated facilitation of noradrenaline release is enhanced by an ongoing activation of alpha2-adrenoceptors. They further suggest that adenosine A 2B-receptors and beta2-adrenoceptors are coupled to distinct adenylyl cyclase isoforms what may explain the different influence of alpha2-adrenoceptor signalling pathway on the facilitatory effects mediated by the two adenylyl cyclase coupled receptors.