Böhle T, Steinbis M, Biskup C, Koopmann R, Benndorf K
Department of Physiology, Friedrich-Schiller-University, D-07740 Jena, Germany.
Biophys J. 1998 Oct;75(4):1740-8. doi: 10.1016/S0006-3495(98)77615-5.
In small cell-attached patches containing one and only one Na+ channel, inactivation was studied in three different gating modes, namely, the fast-inactivating F mode and the more slowly inactivating S mode and P mode with similar inactivation kinetics. In each of these modes, ensemble-averaged currents could be fitted with a Hodgkin-Huxley-type model with a single exponential for inactivation (tauh). tauh declined from 1.0 ms at -60 mV to 0.1 ms at 0 mV in the F mode, from 4.6 ms at -40 mV to 1.1 ms at 0 mV in the S mode, and from 4.5 ms at -40 mV to 0.8 ms at +20 mV in the P mode, respectively. The probability of non-empty traces (net), the mean number of openings per non-empty trace (op/tr), and the mean open probability per trace (popen) were evaluated at 4-ms test pulses. net inclined from 30% at -60 mV to 63% at 0 mV in the F mode, from 4% at -90 mV to 90% at 0 mV in the S mode, and from 2% at -60 mV to 79% at +20 mV in the P mode. op/tr declined from 1.4 at -60 mV to 1.1 at 0 mV in the F mode, from 4.0 at -60 mV to 1.2 at 0 mV in the S mode, and from 2.9 at -40 mV to 1.6 at +20 mV in the P mode. popen was bell-shaped with a maximum of 5% at -30 mV in the F mode, 48% at -50 mV in the S mode, and 16% at 0 mV in the P mode. It is concluded that 1) a switch between F and S modes may reflect a functional change of inactivation, 2) a switch between S and P modes may reflect a functional change of activation, 3) tauh is mainly determined by the latency until the first channel opening in the F mode and by the number of reopenings in the S and P modes, 4) at least in the S and P modes, inactivation is independent of pore opening, and 5) in the S mode, mainly open channels inactivate, and in the P mode, mainly closed channels inactivate.
在仅包含一个钠离子通道的小细胞贴附膜片中，研究了三种不同门控模式下的失活情况，即快速失活的F模式以及失活动力学相似但失活速度较慢的S模式和P模式。在每种模式下，总体平均电流都可以用具有单个失活指数（tauh）的霍奇金-赫胥黎型模型来拟合。在F模式下，tauh从-60 mV时的1.0毫秒降至0 mV时的0.1毫秒；在S模式下，从-40 mV时的4.6毫秒降至0 mV时的1.1毫秒；在P模式下，从-40 mV时的4.5毫秒降至+20 mV时的0.8毫秒。在4毫秒的测试脉冲下评估了非空轨迹的概率（net）、每个非空轨迹的平均开放次数（op/tr）以及每个轨迹的平均开放概率（popen）。在F模式下，net从-60 mV时的30%升至0 mV时的63%；在S模式下，从-90 mV时的4%升至0 mV时的90%；在P模式下，从-60 mV时的2%升至+20 mV时的79%。在F模式下，op/tr从-60 mV时的1.4降至0 mV时的1.1；在S模式下，从-60 mV时的4.0降至0 mV时的1.2；在P模式下，从-40 mV时的2.9降至+20 mV时的1.6。popen呈钟形，在F模式下-30 mV时最大为5%，在S模式下-50 mV时最大为48%，在P模式下0 mV时最大为16%。得出以下结论：1）F模式和S模式之间的转换可能反映了失活的功能变化；2）S模式和P模式之间的转换可能反映了激活的功能变化；3）tauh主要由F模式下直到第一个通道开放的延迟以及S模式和P模式下的重新开放次数决定；4）至少在S模式和P模式下，失活与孔开放无关；5）在S模式下，主要是开放通道失活，在P模式下，主要是关闭通道失活。
