Korogod S M, Kulagina I B
Fiziol Zh (1994). 2012;58(3):50-9.
In computer models, we studied instantaneous (time-varying) current-voltage relationships (iIVs) of populations of ion channels characteristic of the membrane of different type excitable cells, of which the responses to electrical stimuli essentially differ: giant squid axon (Hodgkin-Huxley model), cardiomyocyte, dendrites of CA3 hippocampal pyramidal neurons and Purkinje neurons of the cerebellum. The membrane potential was stepped from the rest level to a certain depolarization test level that was clamped for a certain time, and the total current was measured at different moments after the step onset. For each iIV zero-current points (potentials) were determined. A set of such points, which were situated on the limb of iIV positive slop and corresponded to the state of high membrane depolarization (excitation state, upstate) at different time moments, were used to characterize the dynamics of the excitation state in time. With these indicators the axon membrane was characterized by a single excitation state that rapidly occurred (0.25 ms) and was short-lasting (decayed from -45 to 40 mV during life-time of 5.5 ms). There were two such states of the membrane of cardiomyocyte. The first one was early, rapidly occurring and short-living (rapidly relaxing). It occurred shortly after the depolarization start and lasted for 14.5 ms. The second one was late, slowly rising and long-lasting (occurred with a 7.5-ms delay, increased from 11 to 46 mV in 39 ms and then relaxed lasting for 623 ms in total). The dendritic membrane ofCA3 neurons had one long-lasting excitation state that occurred shortly after the depolarization shift, first rapidly relaxed during 3 ms from initial 30 mV level to -10 mV and then slowly, in 80 ms, stabilized at the level of -20 mV. In the Purkinje neuron membrane two short-lasting and one very long-lasting excitation states were revealed. The first state of very high (>100 mV) depolarization relaxed to 4 mV in 0.8 ms. Shortly before its vanishing, at 0.7 ms, the second short-lasting state emerged, which relaxed in 1 ms from -22 mV to -48 mV. At 1.8 ms a new excitation state emerged, which after a transient relaxation stabilized at -29.65 mV starting from 88 ms. Thus, iIVs allowed disclosing a fine organization of the states of electrical excitation of the membrane and revealing, in populations of ion channels of different content, existence of different number of the mentioned states, which differ from each other in occurrence time and life-time.
在计算机模型中，我们研究了不同类型可兴奋细胞膜上特征性离子通道群体的瞬时（时变）电流-电压关系（iIVs），这些细胞对电刺激的反应本质上有所不同：巨型鱿鱼轴突（霍奇金-赫胥黎模型）、心肌细胞、海马CA3区锥体神经元的树突以及小脑浦肯野神经元。将膜电位从静息水平跃升至某个去极化测试水平，并在该水平钳制一定时间，然后在跃变开始后的不同时刻测量总电流。对于每个iIV，确定零电流点（电位）。一组位于iIV正斜率分支上、对应于不同时刻高膜去极化状态（兴奋状态、上行状态）的此类点，被用于表征兴奋状态随时间的动态变化。利用这些指标，轴突膜的特征是单一的兴奋状态，其快速出现（0.25毫秒）且持续时间短（在5.5毫秒的寿命期间从-45毫伏衰减至40毫伏）。心肌细胞膜有两种这样的状态。第一种是早期的、快速出现且短暂存在的（快速弛豫）。它在去极化开始后不久出现，持续14.5毫秒。第二种是晚期的、缓慢上升且持久的（延迟7.5毫秒出现，在39毫秒内从11毫伏增加到46毫伏，然后总共弛豫持续623毫秒）。CA3神经元的树突膜有一种持久的兴奋状态，在去极化转变后不久出现，最初在3毫秒内从初始的30毫伏水平快速弛豫至-10毫伏，然后在80毫秒内缓慢稳定在-20毫伏水平。在浦肯野神经元膜中，揭示出两种短暂存在的和一种非常持久的兴奋状态。第一种极高（>100毫伏）去极化状态在0.8毫秒内弛豫至4毫伏。在其消失前不久，即0.7毫秒时，出现第二种短暂存在的状态，该状态在1毫秒内从-22毫伏弛豫至-48毫伏。在1.8毫秒时出现一种新的兴奋状态，该状态在短暂弛豫后从88毫秒开始稳定在-29.65毫伏。因此，iIVs能够揭示膜电兴奋状态的精细组织，并在不同成分的离子通道群体中揭示出不同数量的上述状态的存在，这些状态在出现时间和寿命上彼此不同。
