β-blockade abolishes the augmented cardiac tPA release induced by transactivation of heterodimerised bradykinin receptor-2 and β2-adrenergic receptor in vivo

Bradykinin.(BK) receptor-2 (B2R) and beta(2)-adrenergic receptor (beta(2)AR) have been shown to form heterodimers in vitro. However, in vivo proofs of the functional effects of B2R-beta(2)AR heterodimerisation are missing. Both BK and adrenergic stimulation are known inducers of tPA release. Our goal was to demonstrate the existence of B2R-beta(2)AR heterodimerisation in myocardium and to define its functional effect on cardiac release of tPA in vivo. We further investigated the effects of a non-selective beta-blocker on this receptor interplay. To investigate functional effects of B2R-beta(2)AR heterodimerisation (i. e. BK transactivation of beta(2)AR) in vivo, we induced serial electrical stimulation of cardiac sympathetic nerves (SS) in normal pigs that underwent concomitant BK infusion. Both SS and BK alone induced increases in cardiac tPA release. Importantly, despite B2R desensitisation, simultaneous BK infusion and SS (BK+SS) was characterised by 2.3 +/- 0.3-fold enhanced tPA release compared to SS alone. When beta-blockade (propranolol) was introduced prior to BK+SS, tPA release was inhibited. A persistent B2R-beta(2)AR heterodimer was confirmed in BK-stimulated and non-stimulated left ventricular myocardium by immunoprecipitation studies and under non-reducing gel conditions. All together, these results strongly suggest BK transactivation of beta(2)AR leading to enhanced beta(2)AR-mediated release of tPA. Importantly, non-selective P-blockade inhibits both SS-induced release of tPA and the functional effects of B2R-beta(2)AR heterodimerisation in vivo, which may have important clinical implications.