Bradykinin B2-receptor-mediated Stimulation of Exocytotic Noradrenaline Release from Cardiac Sympathetic Neurons

Abstract

Myocardial ischemia, as well as angiotensin-converting-enzyme-inhibitors, increase cardiac concentrations of the non-apeptide bradykinin. Cardiac effects of bradykinin are potentially mediated by modulation of sympathoadrenergic neurotransmission. Accordingly, the present study was designed to examine the influence of bradykinin on exocytotic noradrenaline release from rat isolated perfused heart. Exocytotic noradrenaline release was induced by electrical field stimulation (1 min, 5 V, 6 Hz) twice to compare the effect of intervention (S2) with respective control stimulation (S1). The overflow of endogenous noradrenaline was determined by high pressure liquid chromatography and electrochemical detection. The results are expressed as the mean S2/S1ratio±s.e.m.Bradykinin (1μmol/l) evoked a significant increase in noradrenaline release (S2/S1: 1.60±0.12;P<0.01), which was even more pronounced after inhibition of neuronal reuptake of noradrenaline by desipramine (0.1μmol/l: S2/S1: 1.83±0.15;P<0.01) excluding interference of bradykinin with the noradrenaline uptake1carrier. The concentration–response curve for bradykinin (0.1 nmol/l to 10μmol/l) revealed a maximum effect at 1μmol/l and an EC50-value of 7.5 nmol/l. The effect of bradykinin was unaltered by the B1-receptor antagonist des-Arg9(Leu8)-bradykinin (1μmol/l; S2/S1: 1.69±0.17), whereas it was reduced significantly by the B2-receptor antagonist Hoe 140 (1μmol/l; S2/S1: 1.14±0.11;P<0.05). Des-Arg9-bradykinin (1μmol/l), a specific B1-agonist, had no effect on stimulation-induced noradrenaline release (S2/S1: 0.94±0.08). Utilizing pharmacological interventions, we attempted to characterize the intraneuronal signal transduction pathway mediating the effect of bradykinin on exocytosis. Neither inhibition of cyclooxygenase nor blockade of nitric oxide synthesis affected bradykinin-induced stimulation of noradrenaline release. Likewise, inhibition of protein kinase C by bisindolylmaleimide (1μmol/l) or tyrosine kinase by genistein (10μmol/l) had no effect on the promoting action of bradykinin. In contrast, inhibition of cytosolic phospholipase A2activity by the specific inhibitor AACOCF3(1μmol/l) prevented bradykinin-induced increase in noradrenaline release (S2/S1: 1.09±0.15;P<0.01). In conclusion, bradykinin increases exocytotic release of endogenous noradrenaline from cardiac sympathetic neurons via activation of presynaptic B2-receptors. Intraneuronal coupling of B2-receptors to phospholipase A2appears to mediate the facilitatory effect of bradykinin on noradrenaline release in rat heart.