Santos-Sacchi J
Section of Otolaryngology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Neurosci. 1993 Aug;13(8):3599-611. doi: 10.1523/JNEUROSCI.13-08-03599.1993.
Type I spiral ganglion cells provide the afferent innervation to the inner hair cells of the mammalian organ of Corti and project centrally to the cochlear nucleus. While single-unit studies conducted over the past several decades have provided a wealth of information concerning the response characteristics of these neurons and, to some extent, their receptor targets, little is known about the neuron's intrinsic electrical properties. These properties undeniably will contribute to the firing patterns induced by acoustic stimuli. Type I spiral ganglion cell somata from the guinea pig inner ear were acutely isolated and the voltage-dependent conductances were analyzed with the whole-cell voltage clamp. Under conditions that mimic the normal intra- and extracellular ionic environments, type I spiral ganglion cells demonstrate fast inward TTX-sensitive Na currents (whose current density varied markedly among cells) and somewhat more slowly developing outward K currents. Resting potentials averaged -67.3 mV. Under current clamp, no spontaneous spike activity was noted, but short current injections produced graded action potentials with after hyperpolarizations lasting several milliseconds. The nondecaying outward K current activated at potentials near rest and was characterized by a pronounced rectification. The kinetics of the Na and K currents were rapid. Maximum peak inward Na currents occurred within 400 microseconds, between a voltage range of -10 and 0 mV, and inactivated within 4 msec. Recovery from inactivation was also rapid. At a holding potential of -80 mV, the time constant for recovery from an inactivating voltage step to -10 mV was 2.16 msec. Above -50 mV outward K currents reach half-maximal amplitude within 1.5 msec. In addition to these currents, a slow noninactivating TTX-sensitive inward current was observed that was blockable with Cd2+ or Gd3+. Problems encountered with blocking the tremendous outward K current hampered the characterization of this inward current. Similarities between the kinetics of ganglion cell currents and some of the rapid temporal characteristics of eighth nerve single-unit activity confirm the notion that intrinsic membrane properties help shape auditory neuron responses to sound.
I型螺旋神经节细胞为哺乳动物柯蒂氏器的内毛细胞提供传入神经支配，并向中枢投射至蜗神经核。尽管在过去几十年中进行的单单位研究提供了大量有关这些神经元的反应特性以及在某种程度上其受体靶点的信息，但对于该神经元的内在电特性却知之甚少。这些特性无疑会对声刺激诱发的放电模式产生影响。从豚鼠内耳急性分离出I型螺旋神经节细胞的胞体，并采用全细胞电压钳技术分析其电压依赖性电导。在模拟正常细胞内和细胞外离子环境的条件下，I型螺旋神经节细胞表现出快速内向的河豚毒素敏感钠电流（其电流密度在不同细胞间差异显著）以及发展稍慢的外向钾电流。静息电位平均为-67.3 mV。在电流钳制下未观察到自发的锋电位活动，但短时间电流注入可产生具有持续数毫秒的超极化后电位的分级动作电位。非衰减外向钾电流在接近静息电位时激活，其特征为明显的整流。钠电流和钾电流的动力学过程迅速。最大内向钠电流峰值在400微秒内出现，电压范围在-10至0 mV之间，并在4毫秒内失活。从失活状态恢复也很快。在-80 mV的钳制电位下，从失活电压阶跃到-10 mV的恢复时间常数为2.16毫秒。在-50 mV以上，外向钾电流在1.5毫秒内达到最大幅度的一半。除了这些电流外，还观察到一种缓慢的非失活河豚毒素敏感内向电流，可被Cd2+或Gd3+阻断。由于阻断巨大的外向钾电流存在困难阻碍了对这种内向电流的特性描述。神经节细胞电流动力学与第八对脑神经单单位活动的一些快速时间特性之间的相似性证实了内在膜特性有助于塑造听觉神经元对声音反应的观点。
