Functional analysis of whole cell currents from hair cells of the turtle posterior crista
Functional analysis of whole cell currents from hair cells of the turtle posterior crista
复制标题
DOI：
10.1152/jn.00771.2001
复制
发表时间：
2002-12-01
影响因子：
2.5
通讯作者：
Brichta, AM
中科院分区：
文献类型：
--
作者：
Goldberg, JM;Brichta, AM
控制电流被用来研究电压敏感、向外整流电导的可能功能。结果用线性霍奇金-赫胥黎理论解释。由于I型毛细胞的静息电位更极化，阻抗更低，因此在给定电压下，I型毛细胞需要比II型毛细胞更大的去极化电流。“快速”II型细胞，因其向外电流的快速激活而被称为“快速”II型细胞，在共振频率（最佳）为40-85赫兹的电流阶跃下显示出轻微的欠阻尼响应，远高于自然头部运动的带宽。反映出它们较慢的激活动力学，I型和“慢”II型电池的最佳频率为15-30 Hz，并且调谐不良，严重阻尼或过阻尼。线性化理论确定了影响调谐质量的因素。快速II型毛细胞仅表现出适度的欠阻尼反应，因为它们的稳态I-V曲线不是特别陡峭。我们的I型和缓慢的II型细胞的更差的调谐可以归因于它们缓慢的激活动力学和大的电导。为了研究离子电流如何影响响应动力学，我们将0.1-100 Hz的正弦电流叠加在一个小的去极化稳态电流上，以模拟体内的静息条件。稳定的电流导致缓慢的失活，在快速的II型细胞中最明显，在I型细胞中最不明显。由于失活，快速II型细胞具有几乎被动的响应动力学，低频增益为500-1,000毫欧伽。相比之下，I型细胞和慢速II型细胞在前庭带宽和低频增益分别为20-100和100-500 ω时显示出活跃成分。由于环面和平面快速II型细胞对正弦电流的响应没有差异，电压敏感电流不太可能是支配这两个外周区传入神经的增益和响应动力学的巨大差异的原因。I型细胞的低阻抗和活性成分可能与低增益和适度的含萼传入相响应动力学有关。
Controlled currents were used to study possible functions of voltage-sensitive, outwardly rectifying conductances. Results were interpreted with linearized Hodgkin-Huxley theory. Because of their more hyperpolarized resting potentials and lower impedances, type I hair cells require larger currents to be depolarized to a given voltage than do type II hair cells. "Fast" type II cells, so-called because of the fast activation of their outward currents, show slightly underdamped responses to current steps with resonant (best) frequencies of 40-85 Hz, well above the bandwidth of natural head movements. Reflecting their slower activation kinetics, type I and "slow" type II cells have best frequencies of 15-30 Hz and are poorly tuned, being critically damped or overdamped. Linearized theory identified the factors responsible for tuning quality. Our fast type II hair cells show only modestly underdamped responses because their steady-state I-V curves are not particularly steep. The even poorer tuning of our type I and slow type II cells can be attributed to their slow activation kinetics and large conductances. To study how ionic currents shape response dynamics, we superimposed sinusoidal currents of 0.1-100 Hz on a small depolarizing steady current intended to simulate resting conditions in vivo. The steady current resulted in a slow inactivation, most pronounced in fast type II cells and least pronounced in type I cells. Because of inactivation, fast type II cells have nearly passive response dynamics with low-frequency gains of 500-1,000 MOmega. In contrast, type I and slow type II cells show active components in the vestibular bandwidth and low-frequency gains of 20-100 and 100-500 MOmega, respectively. As there are no differences in the responses to sinusoidal currents for fast type II cells from the torus and planum, voltage-sensitive currents are unlikely to be responsible for the large differences in gains and response dynamics of afferents innervating these two regions of the peripheral zone. The low impedances and active components of type I cells may be related to the low gains and modestly phasic response dynamics of calyx-bearing afferents.