ION CHANNEL TARGETS FOR CARDIAC GLYCOSIDE ACTIONS

强心苷是最广泛使用的强心剂之一， 尽管毒性发生率很高。它们的作用机制被认为是 仅抑制Na，K-ATP酶。其他迫不得已的 然而，有证据表明，其他细胞的行动，包括直接 对肌膜和肌浆网（SR）的作用， 其正性肌力作用和/或毒性作用。这样做的目的 项目是研究几种强心药的新的亚细胞作用 类固醇对心脏离子通道和收缩的调节。 以下是本次续期申请的具体目的：l） 研究SRCRC活动如何受到一些强心药的影响， 类固醇以及这些药物的不同结构成分 （包括内酯环的大小和饱和度， 碳水化合物部分）可能有助于其正性肌力作用; 2)测量强心类固醇改变SRCRC活性的作用 在正常和衰竭的人类心脏中， 事实上可能有助于其在体内的治疗或毒性作用; 3） 以确定细胞内应用不同的强心剂 类固醇引起SR Ca 2+释放增加，这是一种正性肌力作用， 影响和毒性的发展;和4）研究的影响 强心类固醇对动作电位构型和离子电流的影响 为了确定是否对特定的肌膜有直接作用， 离子通道有助于它们的正性肌力和/或毒性 方面的影响. 将使用两种互补的实验方法。单SRCRC 将通过掺入分离自 猫心室，进入人工平面脂质双层。此外，Ca 2 +i 瞬变（用indo-1荧光测量）、离子电流和 在分离的猫心室肌细胞中测量收缩。的 实验将检验以下总体假设： 强心苷通过几种途径产生强心作用。 包括对SR Ca 2+释放的细胞内作用和 对跨膜离子电流的直接影响;这些影响是 独立于，但与他们的已知行动， 抑制肌膜Na，K-ATP酶。 这些实验的结果将有助于确定细胞 心脏正性肌力作用和毒性作用的机制 糖苷界定和区分“非物质文化遗产”的意义 不同强心苷通过SRCRC活性对Ca 2 +i调节的影响 和肌膜离子通道的关系是， 新的代理人，选择性地在这些网站，以保持他们的 有效治疗心脏病，但其毒性继发 对心脏功能的作用可能被削减或取消。

Cardiac glycosides are among the most widely used cardiotonic agents, despite a high incidence of toxicity. Their mechanism of action is thought to be exclusively an inhibition of the Na,K-ATPase. Other compelling evidence, however, suggests additional cellular actions, including direct actions on the sarcolemma and sarcoplasmic reticulum (SR), that contribute to their positive inotropic and/or toxic actions. The purpose of this project is to investigate new subcellular actions of several cardiotonic steroids on regulation of ion channels and contraction in heart. The following are the specific aims of this renewal application: l) to investigate how SRCRC activity is affected by a number of cardiotonic steroids and how the different structural components of these agents (including size and saturation of the lactone ring, presence of the carbohydrate moiety) might contribute to their positive inotropic actions; 2) to measure the effects of cardiotonic steroids to alter SRCRC activity in normal and failing human heart in order to determine if such an action might in fact contribute to its therapeutic or toxic actions in viva; 3) to determine if intracellular application of different cardiotonic steroids causes an increase in SR Ca2+ release, a positive inotropic effect and the development of toxicity; and 4) to study the effects of cardiotonic steroids on action potential configuration and ionic currents in order to determine if there is a direct action on specific sarcolemmal ion channels to contributes to their positive inotropic and/or toxic effects. Two complementary experimental approaches will be used. Single SRCRC activity will be measured by incorporation of SRCRC protein, isolated from cat ventricle, into artificial planar lipid bilayers. In addition, Ca2+i transients (measured with indo-1 fluorescence), ionic currents and contraction will be measured in isolated cat ventricular myocytes. The experiments will test the following Overall Hypothesis: Cardiac glycosides produce their cardiotonic actions via several mechanisms that include an intracellular action on SR Ca2+ release and direct effects on transmembrane ionic currents; these effects are independent from, but work in conjunction with, their known action to inhibit the sarcolemmal Na,K-ATPase. The results of these experiments will help to define the cellular mechanisms for the positive inotropic and toxic actions of cardiac glycosides. The significance of defining and distinguishing between the different cardiac glycoside effects on Ca2+i regulation via SRCRC activity and sarcolemmal ion channels is that it may then be possible to develop new agents that act selectively at these sites to retain their effectiveness in treating cardiac disease but whose toxic secondary actions on cardiac function might be curtailed or abolished.