MODES OF SINGLE NA CHANNEL GATING DURING LATE CURRENTS

蛙骨骼肌单钠通道的初步记录 揭示了钠通道动力学的一种意想不到的复杂性-- 爆发和背景模式的后期钠电流。 这些电流 重要的是要进一步研究，因为它们有重大影响， 建立了钠通道动力学理论。 我们建议研究四个 这些晚期洋流的具体方面： 1.在5-10 kHz时间下测定晚期电流的快速动力学 分辨率 迄今为止的测量是在2 kHz下进行的。 我们 平均开放和关闭时间的估计值由于错过开放而发生偏移 和结案陈词 我们提出了几项改进， 记录，以及组合的单通道波动测量， 我们的时间分辨率 2.测量突发模式的长度和频率，并确定 影响他们的外部因素。 爆发似乎在 通过缓慢的失活过程产生脉冲。 我们的初步工作表明， 突发模式本身可以持续更长的时间。 我们建议比较突发 慢失活的速率。 我们将检查 保持潜力，和细胞质环境的速度， 外观和爆发的长度。 我们也将快速测量 爆发期间的动力学，并将其与给药后观察到的动力学进行比较 的通道与N-溴乙酰胺。 3.进一步检查背景电流是由于 通道从正常失活恢复。 如果背景电流 是由于正常通道从失活恢复，那么它们的动力学 可用于检验钠通道早期电流模型。 但我们的 初步结果表明， 背景电流与电压无关，正如从 这样的模型。 我们将通过比较背景开放来验证这一假设。 早期使用适当参数的寿命和出现率 水流 4.利用爆发和背景海流的动力学信息， 预测钠通道快电流的动力学模型。 我们的假设 关于晚期洋流的起源， 通道动力学简单模型的常数。 我们将确定这些 率，并得出早期电流的形式和大小。 比较 预测和观察到的电流将有助于检查我们的 并建立合理的Na通道模型。

Our preliminary recordings of single Na channels in frog skeletal muscle have brought to light an unsuspected complexity of Na channel kinetics--the bursting and background modes of the late Na currents. These currents are important to study further because they have major implications for established theories of Na channel kinetics. We propose to study four specific aspects of these late currents: 1. Determine the fast kinetics of the late currents at 5-10 kHz time resolution. The measurements to date have been made at 2 kHz. Our estimates of mean open and closed times are shifted due to missed openings and closings in the record. We propose several improvements in our recordings, and a combined single channel-fluctuation measurement to extend our time resolution. 2. Measure the length and frequency of the burst mode, and determine the external factors that influence them. Bursts appear to be ended during pulses by a slow inactivation process. Our preliminary work indicates that the bursting mode itself may last much longer. We propose to compare burst length to the rate of slow inactivation. We will check the influence of holding potential, and of the cytoplasmic environment on the rate of appearance and the length of bursts. We will also measure the fast kinetics during bursts and compare them to those observed after treatment of the channel with N-bromoacetamide. 3. Further check the hypothesis that background currents are due to channels returning from normal inactivation. If the background currents are due to normal channels returning from inactivation, then their kinetics can be used to check models of Na channel's early currents. However, our preliminary results have shown that the rate of appearance of the background currents is not voltage dependent, as might be expected from such a model. We will test this hypothesis by comparing background open lifetimes and rate of appearance with appropriate parameters from the early currents. 4. Use the kinetic information from bursts and background currents to predict a kinetic model of the Na channel's fast currents. Our hypotheses on the origin of the late currents make explicit predictions of the rate constants of simple models of channel kinetics. We will determine these rates, and derive the form and magnitude of the early currents. Comparison of the predicted and the observed currents will serve to check our hypotheses and to establish a reasonable model for the Na channel.