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 mu M) 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 B-2 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 ill 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 B-2-receptor-mediated I-K.ACh inhibition.