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

本申请要求支持继续研究 心肌组织细胞内离子环境。 这很重要 由于细胞内游离Na+（aiNa）和游离Ca ++（aiCa）活性 不是恒定的，而是作为膜电压、刺激 频率和时间;并且可以通过改变 细胞外离子成分和某些药物。 由于Na/Ca 交换系统中，aiNa的变化会导致aiCa的变化， 后果紧张 因此，aiNa的调节可能是重要的 调节心肌收缩力的机制。 将在绵羊中使用离子选择性微电极测量aiNa和aiCa 浦肯野纤维和心室肌制备。 膜电压 (Vm)将使用电压钳进行控制， 紧张局势将受到监测。 aiNa的调节机制将是 在刺激和未刺激的制剂中进行研究。 特别 感兴趣的是，随着年龄的增长， 刺激. 假设它是由Na+通过Na+进入引起的 将通过使用Na+通道阻滞剂TTX和 研究aiNa的频率依赖性升高与 Na+通道稳态失活曲线。 的重要性 Na/K泵的激活水平和细胞外K+的积累， 将通过系统地降低[K]o来研究aiNa的调节。 利用这些方案，aiNa，aiCa， 并且张力可以被拉伸。 此外，当频率依赖性上升时， 在aiNa被Na+通道抑制时，应该可以 修改力-频率曲线。 最后，Na/Ca的耦合比 可以针对宽范围的Vm和稳态计算交换， 非稳态条件。 这些实验将为Na+的调控提供新的信息 和Ca++;离子，直接有助于复杂的力-频率 在心肌中发现的关系。

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.