Locke R E, Nerbonne J M
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Neurophysiol. 1997 Nov;78(5):2309-20. doi: 10.1152/jn.1997.78.5.2309.
Three kinetically distinct Ca2+-independent depolarization-activated K+ currents in callosal-projecting rat visual cortical neurons. J. Neurophysiol. 78: 2309-2320, 1997. Whole cell, Ca2+-independent, depolarization-activated K+ currents were characterized in identified callosal-projecting (CP) neurons isolated from postnatal day 7-16 rat primary visual cortex. CP neurons were identified in vitro after in vivo retrograde labeling with fluorescently tagged latex microbeads. During brief (160-ms) depolarizing voltage steps to potentials between -50 and +60 mV, outward K+ currents in these cells activate rapidly and inactivate to varying degrees. Three distinct K+ currents were separated based on differential sensitivity to 4-aminopyridine (4-AP); these are referred to here as IA, ID, and IK, because their properties are similar (but not identical) K+ currents termed IA, ID, and IK in other cells. The current sensitive to high (>/=100 mu M) concentrations of 4-AP (IA) activates and inactivates rapidly; the current blocked completely by low (</=50 mu M) 4-AP (ID) activates rapidly and inactivates slowly. A slowly activating, slowly inactivating current (IK) remains in the presence of 5 mM 4-AP. IA, ID, and IK also were separated and characterized in experiments that did not rely on the use of 4-AP. All CP cells express all three K+ current types, although the relative densities of IA, ID, and IK vary among cells. The experiments here also have revealed that IA, ID, and IK display similar voltage dependences of activation and steady state inactivation, whereas the kinetic properties of the currents are distinct. At +30 mV, for example, mean +/- SD activation taus are 0. 83 +/- 0.24 ms for IA, 1.74 +/- 0.49 ms for ID, and 14.7 +/- 4.0 ms for IK. Mean +/- SD inactivation taus for IA and ID are 26 +/- 7 ms and 569 +/- 143 ms, respectively. Inactivation of IK is biexponential with mean +/- SD inactivation time constants of 475 +/- 232 ms and 3,128 +/- 1,328 ms; approximately 20% of the 4-AP-insensitive current is noninactivating. For all three components, activation is voltage dependent, increasing with increasing depolarization, whereas inactivation is voltage independent. Both IA and IK recover rapidly from steady state inactivation with mean +/- SD recovery time constants of 38 +/- 7 ms and 79 +/- 26 ms, respectively; ID recovers an order of magnitude more slowly (588 +/- 274 ms). The properties of IA, ID, and IK in CP neurons are compared with those of similar currents described previously in other mammalian central neurons and, in the accompanying paper, the roles of these conductances in regulating the firing properties of CP neurons are explored.
大鼠胼胝体投射视觉皮层神经元中三种动力学特性不同的非钙依赖性去极化激活钾电流。《神经生理学杂志》78: 2309 - 2320, 1997。对从出生后第7 - 16天大鼠初级视觉皮层分离出的已鉴定的胼胝体投射（CP）神经元中的全细胞、非钙依赖性、去极化激活钾电流进行了表征。CP神经元在体内用荧光标记的乳胶微珠进行逆行标记后在体外被鉴定。在短暂（160毫秒）去极化电压阶跃至 - 50至 + 60毫伏之间的电位时，这些细胞中的外向钾电流迅速激活并不同程度地失活。基于对4 - 氨基吡啶（4 - AP）的不同敏感性分离出三种不同的钾电流；这里将它们称为IA、ID和IK，因为它们的特性与其他细胞中称为IA、ID和IK的钾电流相似（但不完全相同）。对高（≥100微摩尔）浓度4 - AP敏感的电流（IA）迅速激活和失活；被低（≤50微摩尔）4 - AP完全阻断的电流（ID）迅速激活且缓慢失活。在存在5毫摩尔4 - AP的情况下，一种缓慢激活、缓慢失活的电流（IK）仍然存在。IA、ID和IK也在不依赖于使用4 - AP的实验中被分离和表征。所有CP细胞都表达所有三种钾电流类型，尽管IA、ID和IK的相对密度在不同细胞中有所变化。这里的实验还表明，IA、ID和IK表现出相似的激活电压依赖性和稳态失活，而电流的动力学特性是不同的。例如，在 + 30毫伏时，IA的平均±标准差激活时间常数为0.83±0.24毫秒，ID为1.74±0.49毫秒，IK为14.7±4.0毫秒。IA和ID的平均±标准差失活时间常数分别为26±7毫秒和569±143毫秒。IK的失活是双指数的，平均±标准差失活时间常数为475±232毫秒和3128±1328毫秒；约20%的对4 - AP不敏感的电流是不发生失活的。对于所有三个成分，激活是电压依赖性的，随着去极化增加而增加，而失活是电压不依赖性的。IA和IK都从稳态失活中迅速恢复，平均±标准差恢复时间常数分别为38±7毫秒和79±26毫秒；ID恢复得慢一个数量级（588±274毫秒）。将CP神经元中IA、ID和IK的特性与先前在其他哺乳动物中枢神经元中描述的类似电流的特性进行了比较，并在随附的论文中探讨了这些电导在调节CP神经元放电特性中的作用。
