NA+, CA++, AND TENSION IN VOLTAGE CLAMPED CARDIAC MUSCLE

本申请请求支持继续研究 心脏组织的细胞内离子环境。这事很重要 因为细胞内游离钠离子(AINA)和游离钙离子(AICA)活性 不是恒定的，而是作为膜电压、刺激的函数而变化的 频率和时间；并且可以通过更改 细胞外离子组成和某些药物。因为钠/钙 交易所系统，AINA的变化产生了AICA和AS的变化 后果就是紧张。因此，对AINA的调节可能是一个重要的 心肌收缩能力的调节机制。 用离子选择微电极测定绵羊体内的AINA和AICA 浦肯野纤维和心室肌制剂。膜电压 (Vm)将使用电压钳位进行控制，并且休眠和相控 紧张局势将受到监控。AINA的调控机制将是 在刺激性和非刺激性制剂中进行研究。特别的 兴趣是AINA的频率依赖的上升，发生在 刺激。认为它是通过Na+进入体内的假说 将通过使用钠离子通道阻滞剂TTX和通过 AINA频率依赖性上升与AINA的关系研究 Na+通道稳态失活曲线。重要的一点是 Na/K泵的激活水平与细胞外K+的积累 AINA的调节将通过系统降低[K]O来研究。 通过这些方案，AINA、AICA、 而紧张可能会被拉上来。此外，当频率依赖性增加时 在AINA中被钠离子通道抑制，应该是有可能的 修改力-频率曲线。最后，Na/Ca的偶联比 可以针对大范围的VM和稳定状态计算交换 非稳态条件。 这些实验将为Na+的调节提供新的信息 和Ca++离子直接对复数作用力频率有贡献 在心肌中发现的联系。

This application requests support for the continued study of the intracellular ionic environment in cardiac tissue. This is important because the intracellular free-Na+ (aiNa) and free-Ca++ (aiCa) activities are not constant, but vary as a function of membrane voltage, stimulation frequency, and time; and can be modified by alterations in the extracellular ionic composition and by certain drugs. Because of the Na/Ca exchange system, changes in aiNa produce changes in aiCa and as a consequence, tension. Thus, modulation of aiNa may be an important mechanism in the regulation of contractility in cardiac muscle. aiNa and aiCa will be measured with ion-selective microelectrodes in sheep Purkinje fiber and ventricular muscle preparations. The membrane voltage (Vm) will be controlled using a voltage clamp, and resting and phasic tension will be monitored. The mechanism of regulation of aiNa will be investigated in stimulated and unstimulated preparations. Of particular interest is the frequency dependent rise in aiNa that occurs with stimulation. The hypothesis that it results from Na+ entry via the Na+ channel will be tested by the use of the Na+ channel blocker TTX, and by studying the relationship between the frequency dependent rise in aiNa and the Na+ channel steady state inactivation curve. The importance of the level of activation of the Na/K pump and extracellular K+ accumulation in the regulation of aiNa will be studied by systematically reducing [K]o. With these protocols, temporal correlations between changes in aiNa, aiCa, and tension may be drawn. Furthermore, where the frequency dependent rise in aiNa is suppressed by Na+ channel inhibition, it should be possible to modify the force-frequency curve. Lastly, the coupling ratio for Na/Ca exchange may be calculated for a wide range of Vm and for steady state and non-steady state conditions. These experiments will provide new information about the regulation of Na+ and Ca++; ions that contribute directly to the complex force-frequency relationship found in cardiac muscle.