Eatock R A, Rüsch A, Lysakowski A, Saeki M
Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Texas 77030, USA.
Otolaryngol Head Neck Surg. 1998 Sep;119(3):172-81. doi: 10.1016/S0194-5998(98)70052-X.
Two morphological classes of mechanosensory cells have been described in the vestibular organs of mammals, birds, and reptiles: type I and type II hair cells. Type II hair cells resemble hair cells in other organs in that they receive bouton terminals from primary afferent neurons. In contrast, type I hair cells are enveloped by large cuplike afferent terminals called calyces. Type I and II cells differ in other morphological respects: cell shape, hair bundle properties, and more subtle ultrastructural features. Understanding the functional significance of these strikingly different morphological features has proved to be a challenge. Experiments that correlated the response properties of primary vestibular afferents with the morphologies of their afferent terminals suggested that the synapse between the type I hair cell and calyx ending is lower gain than that between a type II hair cell and a bouton ending. Recently, patch-clamp experiments on isolated hair cells have revealed that type I hair cells from diverse species have a large potassium conductance that is activated at the resting potential. As a consequence, the voltage responses generated by the type I hair cells in response to injected currents are smaller than those generated by type II hair cells. This may contribute to the lower gain of type I inputs to primary afferent neurons. Studies of neonatal mouse utricles show that the type I-specific potassium conductance is not present at birth but emerges during the first postnatal week, a period of morphological differentiation of type I and type II hair cells.
在哺乳动物、鸟类和爬行动物的前庭器官中，已描述了两种形态学类型的机械感觉细胞：I型和II型毛细胞。II型毛细胞类似于其他器官中的毛细胞，因为它们接受来自初级传入神经元的终扣终末。相比之下，I型毛细胞被称为壶腹的大型杯状传入终末所包绕。I型和II型细胞在其他形态学方面也存在差异：细胞形状、毛束特性以及更细微的超微结构特征。事实证明，理解这些显著不同的形态学特征的功能意义是一项挑战。将初级前庭传入神经的反应特性与其传入终末的形态相关联的实验表明，I型毛细胞与壶腹终末之间的突触增益低于II型毛细胞与终扣终末之间的突触增益。最近，对分离的毛细胞进行的膜片钳实验表明，来自不同物种的I型毛细胞具有在静息电位时被激活的大钾电导。因此，I型毛细胞对注入电流产生的电压反应小于II型毛细胞产生的电压反应。这可能导致I型向初级传入神经元输入的增益较低。对新生小鼠椭圆囊的研究表明，I型特异性钾电导在出生时并不存在，而是在出生后的第一周出现，这是I型和II型毛细胞形态分化的时期。
