Genistein Increases the Sensitivity of Cardiac Ion Channels to beta-Adrenergic Receptor Stimulation

• Published in: Circulation research 1998-07, Vol.83 (1), p.33-42
• Main Authors: Hool, Livia C, Middleton, Lisa M, Harvey, Robert D
• Format: Article
• Language: English
• Subjects: Adrenergic beta-Agonists - pharmacology; Animals; Biological and medical sciences; Calcium - physiology; Cell physiology; Chlorides - physiology; Cyclic AMP - physiology; Cystic Fibrosis Transmembrane Conductance Regulator - physiology; Electric Conductivity; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; Genistein - pharmacology; Guinea Pigs; Ion Channels - drug effects; Isoproterenol - pharmacology; Membrane and intracellular transports; Molecular and cellular biology; Myocardium - metabolism; Patch-Clamp Techniques; Potassium - physiology; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - physiology
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.83.1.33

The whole-cell patch-clamp technique was used to monitor the effects of genistein, a tyrosine kinase inhibitor, on membrane currents recorded from isolated guinea pig ventricular myocytes. Under control conditions, genistein (50 [micro sign]mol/L) did not activate the latent cAMP-regulated Cl current (ICl). However, in the presence of a subthreshold concentration (1 nmol/L) of the beta-adrenergic agonist isoproterenol (Iso), genistein caused a near-maximal activation of this current. In the absence of genistein, Iso activated ICl with an EC50 of 5 nmol/L. In the presence of genistein, Iso activated ICl with an EC50 of 0.3 nmol/L. This facilitatory effect was not observed in the presence of daidzein (50 [micro sign]mol/L), an analogue of genistein that only weakly inhibits tyrosine kinase activity. Furthermore, peroxovanadate, a potent inhibitor of phosphotyrosine phosphatase activity, inhibited ICl activated by Iso alone, and it blocked the stimulatory effect of genistein in the presence of Iso. To determine whether the stimulatory effect of genistein was specific for ICl, we also studied its action on the cAMP-regulated delayed rectifier K current (IK) and L-type Ca current (ICa-L) present in these cells. Basal IK and ICa-L were partially ([=approximate]30% to 40%) inhibited by genistein. However, this inhibitory effect was mimicked by daidzein, suggesting that inhibition of tyrosine kinase activity is not involved. In addition to the nonspecific inhibitory effect, genistein also caused a significant increase in the beta-adrenergic sensitivity of the unblocked cationic currents. In the absence of genistein, 1 nmol/L Iso had no effect on either IK or ICa-L. However, in the presence of genistein, 1 nmol/L Iso significantly increased the magnitude of both currents. These results suggest that tyrosine kinase activity may play an important role in regulating beta-adrenergic responsiveness of the heart. (Circ Res. 1998;83:33-42.)