Jansen J K, Nicholls J G
J Physiol. 1973 Mar;229(3):635-55. doi: 10.1113/jphysiol.1973.sp010158.
Following trains of impulses, sensory neurones in the C.N.S. of the leech show a prolonged hyperpolarization, which lasts for seconds or minutes. In the present investigation the mechanisms that underly this hyperpolarization have been studied by recording intracellularly. Two factors have been found to be responsible. One is the activity of an electrogenic pump (see Baylor & Nicholls, 1969b); the other is a long-lasting change in K conductance.1. Additional evidence that an electrogenic pump contributes to a slow after-hyperpolarization of leech sensory neurones is provided by the effects of injecting Na intracellularly. This leads to an increase in membrane potential that is blocked by the cardiac glycoside strophanthidin. Furthermore, after a train of impulses, reducing the K concentration in the external fluid characteristically reduces the hyperpolarizing action of the pump.2. The hyperpolarization following impulses is associated with a reduction of the cell membrane resistance that can persist for several minutes.3. Several lines of evidence suggest that the reduction in input resistance during the hyperpolarization is mainly due to an increased permeability to K. Thus, when the K concentration in Ringer fluid is reduced, the peak amplitude of the hyperpolarization following a train becomes larger. Furthermore, the conductance dependent part of the after-hyperpolarization has a reversal potential close to the equilibrium potential for K (E(K)). Substitution of Cl by SO(4) has little effect either on the after-hyperpolarization or on the conductance change following a train.4. Increased external Ca concentrations lead to a marked increase in the hyperpolarization that follows impulse activity. The enhanced hyperpolarization in high Ca is associated with a corresponding reduction in input resistance. The amplitude and duration of the hyperpolarization following a brief train of impulses can be increased by a factor of 5 or more in Ringer fluid containing 10 mM-Ca instead of the usual 1.8 mM. The hyperpolarization and resistance changes still occur in solutions containing 20 mM-Mg.5. To augment the hyperpolarization the increased concentration of Ca must be present during the train of impulses.6. The relative contributions of the K conductance increase and of the electrogenic pump for generating the hyperpolarization after impulse activity are different in the three types of sensory cell responding to touch, pressure and noxious stimulation.
在一连串冲动之后，水蛭中枢神经系统中的感觉神经元会出现持续数秒或数分钟的超极化。在本研究中，通过细胞内记录对这种超极化的潜在机制进行了研究。发现有两个因素起作用。一个是生电泵的活动（见贝勒和尼科尔斯，1969b）；另一个是钾离子电导的持久变化。
向细胞内注射钠离子的效应提供了额外证据，证明生电泵促成了水蛭感觉神经元的缓慢后超极化。这会导致膜电位升高，而这种升高会被强心苷毒毛花苷所阻断。此外，在一连串冲动之后，降低细胞外液中的钾离子浓度会典型地降低泵的超极化作用。
冲动后的超极化与细胞膜电阻的降低有关，这种降低可持续数分钟。
几条证据表明，超极化期间输入电阻的降低主要是由于对钾离子的通透性增加。因此，当林格液中的钾离子浓度降低时，一连串冲动后的超极化峰值幅度会变大。此外，后超极化的电导依赖性部分的反转电位接近钾离子的平衡电位（E(K)）。用硫酸根取代氯离子对后超极化或一连串冲动后的电导变化几乎没有影响。
细胞外钙离子浓度增加会导致冲动活动后超极化显著增加。高钙条件下增强的超极化与输入电阻的相应降低有关。在含有10 mM钙离子而非通常的1.8 mM钙离子的林格液中，短暂的一连串冲动后的超极化幅度和持续时间可增加5倍或更多。在含有20 mM镁离子的溶液中，超极化和电阻变化仍然会发生。
为了增强超极化，在一连串冲动期间必须存在增加的钙离子浓度。
在对触觉、压力和有害刺激作出反应的三种感觉细胞中，钾离子电导增加和生电泵对冲动活动后产生超极化的相对贡献有所不同。
