Inhibition of L-type Calcium Current in Rat Ventricular Cells by the Tyrosine Kinase Inhibitor, Genistein and its Inactive Analog, Daidzein

• Published in: Journal of molecular and cellular cardiology 1996-04, Vol.28 (4), p.807-814
• Main Authors: Yokoshiki, Hisashi, Sumii, Kotaro, Sperelakis, Nicholas
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; Ca 2+current; Calcium Channels - metabolism; Calcium Channels - physiology; Cardiomyocytes; Cells, Cultured; Daidzein inhibition; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Genistein; Genistein inhibition; Heart Ventricles - cytology; Heart Ventricles - metabolism; In Vitro Techniques; Isoflavones - pharmacology; Newborn rat heart; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - metabolism; Rats; Time Factors; Tyrosine kinase activity; Ventricular Function; Whole-cell voltage clamp
• ISSN: 0022-2828; 1095-8584
• DOI: 10.1006/jmcc.1996.0075

Effects of genistein, a specific inhibitor of tyrosine kinase, on the l-type Ca 2+channels were examined in freshly isolated young (days 10–18) rat ventricular cells using the whole-cell patch-clamp technique. Bath application of genistein decreased the l-type Ca 2+current [I Ca(L)] in a concentration-dependent manner. The maximal inhibition of I Ca(L)was about 40% (attained at concentrations above 100 μ m); the concentration for half-inhibition (IC 50) was 11 μ m. The effect of genistein (applied for about 5 min) was poorly reversible after washout for up to 5 min. The potential for half-inhibition (V h) of the steady-state inactivation curve was shifted in the negative direction by 7 mV (at 100 μ m) by genistein, and the slope factor was also slightly changed; the activation curve was not affected. Daidzein, which is structurally related to genistein, but has little inhibitory effect on tyrosine kinase activity (of the EGF receptor), unexpectedly had almost the same inhibitory effect on I Ca(L). These observations suggest two possibilities for modulation of I Ca(L)in rat ventricular cells by genistein: (a) phosphorylation of the slow Ca 2+channels by tyrosine kinase; and (b) direct inhibition of the slow Ca 2+channels (i.e. independent of inhibition of tyrosine kinase activity).