KINETICS AND STEADY-STATE PROPERTIES OF CHARGED SYSTEM CONTROLLING SODIUM CONDUCTANCE IN SQUID GIANT-AXON
KINETICS AND STEADY-STATE PROPERTIES OF CHARGED SYSTEM CONTROLLING SODIUM CONDUCTANCE IN SQUID GIANT-AXON
复制标题
DOI：
10.1113/jphysiol.1974.sp010575
复制
发表时间：
1974-01-01
影响因子：
5.5
通讯作者：
ROJAS, E
中科院分区：
文献类型：
--
作者：
KEYNES, RD;ROJAS, E
1. 在鱿鱼巨型轴突中，研究了在两个方向施加等电压箝位脉冲后，位移电流通过膜的早期过程中的不对称性。在进行测量之前，通过去除外部Na和用河豚毒素处理来阻断Na电流。钾电流通常通过灌注脑脊液阻断，但一些实验是在完整的轴突上进行的。采用信号平均技术消除了膜电流的对称分量。不对称电流对薄膜中移动电荷或偶极子的运动有相当大的贡献。这表现为向外的电流在膜去极化时迅速上升到峰值，然后呈指数下降至零，随后在脉冲结束时出现向内的电流浪涌，其时间过程相似。脉冲期间也有持续的电流向外流动，这是由具有整流特性的离子泄漏引起的。在脉冲开始和结束时，电荷的总转移量相等且相反，当内电位达到足够的正值时，它达到饱和，并且它的大小不受温度的影响，尽管它的时间常数有很大的温度系数，这些证明支持了指数变化的电流分量的识别。在稳定状态下，移动电荷的分布服从玻尔兹曼分布。在分布曲线的中点，当电位变化19 mV时，电荷位移的比例发生了e倍的变化。粒子的有效价，即它们的实际电荷乘以作用在它们身上的电场的分数，因此是1·3.5。在0.05 cm2的膜上，总电荷量约为1500 × 10−12C，约为1900个电荷/μm2.6。这些移动电荷与控制钠电导的门控粒子的识别得到了以下发现的支持：(a)它们的时间常数与霍奇金和赫胥黎的“m”系统的时间常数相同，无论是绝对值还是它们对电位和温度的依赖，(b)电荷均匀分布在膜两侧的过渡电位也与完整轴突中的“m”系统一致。内部离子强度的降低或外部钙离子浓度的提高也会使其值向正方向移动。(c)对控制移动电荷稳态分布和Na电导率的曲线的陡峭度的比较表明，3组电荷的有效合作涉及其中，再次与“m”系统非常一致。在5-8的范围内，移动电荷的位移不受外部pH的影响，但初步观察表明，1%的普鲁卡因将总电荷转移减少到不到初始值的40%，并且大约减少了一半的时间常数。
1. Asymmetries in the early time course of the displacement current passing across the membrane after application of equal voltage‐clamp pulses in the two directions have been investigated in the squid giant axon. Before making the measurements, Na current was blocked by removal of external Na and treatment with tetrodotoxin. Potassium current was usually blocked by perfusion with CsF, but some experiments were done with intact axons. A signal averaging technique was used to eliminate the symmetrical components of the membrane current.2. The asymmetrical current had a contribution of appreciable size attributed to the movement of mobile charges or dipoles in the membrane. This was manifested as an outward current rising rapidly to a peak on depolarization of the membrane and then declining exponentially to zero, followed at the end of the pulse by an inward surge of current with a similar time course. There was also a sustained flow of current outwards during the pulse, arising from ionic leakage with a rectifying characteristic.3. The identification of the exponentially changing current component with the displacement of charged particles forming an integral part of the membrane was supported by the demonstration that the total transfer of charge was equal and opposite at the beginning and end of the pulse, that it reached saturation when the internal potential was taken to a sufficient positive value, and that its size was unaffected by temperature, although its time constant had a large temperature coefficient.4. The disposition of the mobile charges in the steady state was shown to obey a Boltzmann distribution. At the midpoint of the distribution curve, the proportion of the charge displaced underwent an e‐fold change for a 19 mV change in potential. The effective valency of the particles, that is their actual charge multiplied by the fraction of the electric field acting on them, was therefore 1·3.5. The total quantity of mobile charge was estimated as about 1500 × 10−12C for 0·05 cm2of membrane, corresponding to some 1900 charges/μm2.6. The identification of these mobile charges with the gating particles responsible for controlling Na conductance was supported by the findings that (a) their time constants were the same as those of Hodgkin & Huxley's ‘m’ system, both in absolute magnitude and in their dependence on potential and temperature, (b) the transition potential at which the charges were evenly distributed on the two sides of the membrane also agreed with that for the ‘m’ system in intact axons, and its value was similarly shifted in a positive direction by a reduction in internal ionic strength or by raising the external Ca concentration, (c) comparison of the steepness of the curves governing on the one hand the steady‐state distribution of the mobile charges and on the other the Na conductance, suggested that an effective cooperation of the charges in groups of three was involved, again in excellent agreement with the ‘m’ system.7. Displacement of the mobile charges was unaffected by external pH over the range 5–8, but preliminary observations showed that 1% procaine reduced the total charge transfer to somewhat less than 40% of the initial value, and roughly halved the time constant.