Bradykinin B 2 ‐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 n M ) increased the L‐type Ca 2+ 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 EC 50 value for increasing I Ca was 5.2 n M . 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 μ M ) with an EC 50 value of 0.57 n M . 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 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 B 2 ‐receptor‐mediated I K.ACh inhibition.British Journal of Pharmacology (1998) 125 , 283–292; doi: 10.1038/sj.bjp.0702060