Bradykinin B2 receptor-mediated chronotropic effect of bradykinin in isolated guinea pig atria

Bradykinin B2-receptor-mediated positive chronotropic effect of bradykinin in isolated rat atria

The positive chronotropic effect of bradykinin was investigated in isolated spontaneously beating atria of the rat. Cumulative additions of bradykinin (0.3-100 nM) caused a concentration-dependent increase in the beating rate of the atria by maximally 35+/-4 beats/min, approximately 25% of the 1 microM isoprenaline-induced maximal responses. In contrast, the active metabolite of bradykinin and selective bradykinin B1-receptor agonist, Des-Arg9-bradykinin, did not influence the spontaneous frequency of beating. Propranolol (1 microM) combined with prazosin (1 microM) did not affect the positive chronotropic effect of bradykinin. A selective bradykinin B2-receptor antagonist, Hoe 140, concentration-dependently shifted the response curves for bradykinin to the right, whereas the bradykinin B1-receptor antagonist, Lys-[Leu8]Des-Arg9-bradykinin had no effect. The tachycardic responses to bradykinin were potentiated by ramipril, an angiotensin-converting enzyme/kininase II inhibitor, but not affected by Nomega-nitro-L-arginine methyl ester hydrochloride, a nitric oxide synthesis inhibitor. Indomethacin and meclofenamate, two cyclooxygenase inhibitors, abolished the bradykinin-induced chronotropic effect. These results indicate that exogenous bradykinin induces a positive chronotropic effect that occurs independent of adrenoceptors. The bradykinin-induced chronotropic effect is mediated by bradykinin B2 receptors, whereas B1 receptors do not play a role in mediating this effect. Prostaglandins but not nitric oxide appear to be involved in bradykinin-induced positive chronotropic effect.

Bradykinin B2-receptor-mediated modulation of membrane currents in guinea-pig cardiomyocytes

1. In order to define the electrophysiological mechanism(s) responsible for bradykinin (BK)-induced positive inotropic and chronotropic responses in isolated guinea-pig atria, effects of BK on the membrane currents were examined in isolated atrial cells using patch clamp techniques. 2. BK (0.1-1000 nM) increased the L-type Ca2+ current (I(Ca)), which was recorded from enzymatically-dissociated atrial myocytes by the nystatin-perforated patch method, in a concentration-dependent fashion, and the calculated EC50 value for increasing I(Ca) was 5.2 nM. In conventional ruptured patch experiments, BK inhibited the muscarinic acetylcholine receptor-operated K+ current (I(K.ACh)) that was activated by the muscarinic agonist carbachol (1 microM) with an EC50 value of 0.57 nM. Both the increase in I(Ca) and the decrease in I(K.ACh) were blocked by HOE140, a selective bradykinin B2 receptor antagonist. 3. The BK-induced inhibition of I(K.ACh) was significantly attenuated by staurosporine and calphostin C, protein kinase C inhibitors. In addition, the I(K.ACh) inhibition by BK was also attenuated by the tyrosine kinase inhibitor genistein or tyrphostin but not by daidzein, an inactive analogue of genistein. However, neither protein kinase C inhibitor nor tyrosine kinase inhibitor affected the BK-induced increase in I(Ca). 4. In the presence and absence of muscarinic stimulation, BK prolonged the action potential recorded from the atrial cells in the current clamp mode. 5. We conclude that BK increases I(Ca) and decreases I(K.ACh) in atrial cells, resulting in positive inotropic and chronotropic responses in atrial preparations. Protein kinase C activation, and possibly tyrosine kinase activation, may be involved in the B2-receptor-mediated I(K.ACh) inhibition.

Positive chronotropic activity of bradykinin in the pithed normotensive rat

The positive chronotropic effect of bradykinin was investigated in the pithed rat preparation. Cumulative treatment with bradykinin (0.20 nmol/kg-6.59 mumol/kg, intravenous [i.v.]) caused a dose-dependent increase in heart rate (HR) by a maximum of 80 +/- 3.3 beats min-1. In contrast, the active metabolite of bradykinin and selective bradykinin B1-receptor agonist, [des-Arg9]-bradykinin did not influence the spontaneous frequency of beating. Propranolol alone reduced the bradykinin-induced increase in HR and a combination of propranolol with prazosin abolished the chronotropic effect of bradykinin. The selective bradykinin B2 receptor antagonist. Hoe 140, dose-dependently shifted the dose-response curves of bradykinin to the right, whereas the bradykinin B1 receptor antagonist, des-Arg10-[Leu9]-kallidin proved ineffective. From our experiments it may be concluded that bradykinin induces tachycardia in the pithed rat primarily by stimulating the sympathetic ganglia leading to the release of noradrenaline, which subsequently activates cardiac beta 1-adrenoceptors. The bradykinin-induced chronotropic effect is mediated by bradykinin B2-receptors, whereas B1-receptors appear not to be involved.