Yokoshiki H, Sumii K, Sperelakis N
Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, Ohio 45267, USA.
J Mol Cell Cardiol. 1996 Apr;28(4):807-14. doi: 10.1006/jmcc.1996.0075.
Effects of genistein, a specific inhibitor of tyrosine kinase, on the L-type Ca2+ 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 Ca2+ current [I(Ca(L))] in a concentration-dependent manner. The maximal inhibition of I(Ca(L)) was about 40% (attained at concentrations above 100 microM); the concentration for half-inhibition (IC50) was 11 microM. The effect of genistein (applied for about 5 min) was poorly reversible after washout for up to 5 min. The potential for half-inhibition (Vh) of the steady-state inactivation curve was shifted in the negative direction by 7 mV (at 100 microM) 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 Ca2+ channels by tyrosine kinase; and (b) direct inhibition of the slow Ca2+ channels (i.e. independent of inhibition of tyrosine kinase activity).
利用全细胞膜片钳技术，在新鲜分离的幼年（10 - 18日龄）大鼠心室细胞中研究了酪氨酸激酶特异性抑制剂染料木黄酮对L型Ca2+通道的作用。浴槽中加入染料木黄酮可使L型Ca2+电流[I(Ca(L))]呈浓度依赖性降低。I(Ca(L))的最大抑制率约为40%（在浓度高于100 microM时达到）；半数抑制浓度（IC50）为11 microM。染料木黄酮作用约5分钟后，洗脱长达5分钟，其作用恢复较差。染料木黄酮使稳态失活曲线的半数抑制电位（Vh）向负向移动7 mV（在100 microM时），斜率因子也略有变化；激活曲线未受影响。大豆苷元与染料木黄酮结构相关，但对（表皮生长因子受体的）酪氨酸激酶活性几乎没有抑制作用，却意外地对I(Ca(L))有几乎相同的抑制作用。这些观察结果提示染料木黄酮对大鼠心室细胞中I(Ca(L))的调节有两种可能：（a）酪氨酸激酶对慢Ca2+通道的磷酸化作用；（b）对慢Ca2+通道的直接抑制作用（即与酪氨酸激酶活性的抑制无关）。
