Brichta Alan M, Aubert Anne, Eatock Ruth Anne, Goldberg Jay M
Department of Otolaryngology-Head and Neck Surgery, Pharmacology and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
J Neurophysiol. 2002 Dec;88(6):3259-78. doi: 10.1152/jn.00770.2001.
The turtle posterior crista is made up of two hemicristae, each consisting of a central zone containing type I and type II hair cells and a surrounding peripheral zone containing only type II hair cells and extending from the planum semilunatum to the nonsensory torus. Afferents from various regions of a hemicrista differ in their discharge properties. To see if afferent diversity is related to the basolateral currents of the hair cells innervated, we selectively harvested type I and II hair cells from the central zone and type II hair cells from two parts of the peripheral zone, one near the planum and the other near the torus. Voltage-dependent currents were studied with the whole cell, ruptured-patch method and characterized in voltage-clamp mode. We found regional differences in both outwardly and inwardly rectifying voltage-sensitive currents. As in birds and mammals, type I hair cells have a distinctive outwardly rectifying current (I(K,L)), which begins activating at more hyperpolarized voltages than do the outward currents of type II hair cells. Activation of I(K,L) is slow and sigmoidal. Maximal outward conductances are large. Outward currents in type II cells vary in their activation kinetics. Cells with fast kinetics are associated with small conductances and with partial inactivation during 200-ms depolarizing voltage steps. Almost all type II cells in the peripheral zone and many in the central zone have fast kinetics. Some type II cells in the central zone have large outward currents with slow kinetics and little inactivation. Although these currents resemble I(K,L), they can be distinguished from the latter both electrophysiologically and pharmacologically. There are two varieties of inwardly rectifying currents in type II hair cells: activation of I(K1) is rapid and monoexponential, whereas that of I(h) is slow and sigmoidal. Many type II cells either have both inward currents or only have I(K1); very few cells only have I(h). Inward currents are less conspicuous in type I cells. Type II cells near the torus have smaller outwardly rectifying currents and larger inwardly rectifying currents than those near the planum, but the differences are too small to account for variations in discharge properties of bouton afferents innervating the two regions of the peripheral zone. The large outward conductances seen in central cells, by lowering impedances, may contribute to the low rotational gains of some central-zone afferents.
龟的后半规管嵴由两个半规管嵴组成，每个半规管嵴都由一个中央区和一个周围的外周区组成，中央区包含I型和II型毛细胞，外周区仅包含II型毛细胞，从半月平面延伸至非感觉性隆凸。来自一个半规管嵴不同区域的传入神经在其放电特性上存在差异。为了探究传入神经的多样性是否与所支配毛细胞的基底外侧电流有关，我们从中央区选择性地采集了I型和II型毛细胞，并从外周区的两个部分采集了II型毛细胞，一部分靠近半月平面，另一部分靠近隆凸。采用全细胞破裂膜片法研究电压依赖性电流，并在电压钳模式下进行特性分析。我们发现外向整流和内向整流电压敏感电流均存在区域差异。与鸟类和哺乳动物一样，I型毛细胞具有独特的外向整流电流（I(K,L)），其在比II型毛细胞外向电流更超极化的电压下开始激活。I(K,L)的激活缓慢且呈S形。最大外向电导较大。II型细胞的外向电流在激活动力学方面存在差异。具有快速动力学的细胞与小电导相关，并且在200毫秒去极化电压阶跃期间会部分失活。外周区几乎所有的II型细胞以及中央区的许多II型细胞都具有快速动力学。中央区的一些II型细胞具有大的外向电流，动力学缓慢且几乎不失活。尽管这些电流类似于I(K,L)，但在电生理学和药理学上都可以将它们与I(K,L)区分开来。II型毛细胞中有两种内向整流电流：I(K1)的激活迅速且呈单指数形式，而I(h)的激活缓慢且呈S形。许多II型细胞要么同时具有这两种内向电流，要么仅具有I(K1)；很少有细胞仅具有I(h)。I型细胞中的内向电流不太明显。靠近隆凸的II型细胞比靠近半月平面的II型细胞具有更小的外向整流电流和更大的内向整流电流，但这些差异太小，无法解释支配外周区两个区域的终扣传入神经放电特性的变化。中央区细胞中所见的大外向电导通过降低阻抗，可能有助于某些中央区传入神经的低旋转增益。
