Housley G D, Norris C H, Guth P S
Tulane University School of Medicine, Department of Pharmacology, New Orleans, Louisiana 70112.
Hear Res. 1989 Apr;38(3):259-76. doi: 10.1016/0378-5955(89)90070-1.
Hair cells isolated from the crista ampullaris of the frog (Rana pipiens) remained viable for up to 5 h and were studied using whole cell voltage- and current clamp recordings. Morphological characteristics of isolated crista hair cells were compared with hair cells studied in situ using light- and electron microscopy. While other labyrinthine hair cells such as mammalian inner and outer hair cells of the cochlea, saccular hair cells of the frog, and cochlear hair cells of the turtle typically have a cylindrical shape, the crista hair cells in the frog are predominantly bulbous, having a thin elongated trunk projecting from a spherical base just large enough to enclose the nucleus. This shape correlates well with the compressed packing configuration of hair cells of the crista ampullaris observed in situ in the histological material. The support cells often failed to separate adjacent hair cells, particularly the apical ends of the hair cells. Maximal cell density on the sensory epithelial ridge appears to be achieved by this arrangement. The mean resting membrane potential (Vz) of isolated crista hair cells was -44.8 mV. Cells with smooth surfaces and apparent opacity had the most negative Vz potentials. As the cells appeared to deteriorate, there was development of transparency and cell surface granulation. Such cells had more positive initial Vz values. Cells with Vz values more positive than -15 mV exhibited a distinct, contoured nucleus. Cells lacking these indicators of deterioration were characterized by input resistances of 1.9 +/- 0.31 G omega and membrane time constants of 13 +/- 2.5 ms. A large complex outwardly rectifying current was identified which was abolished by substituting Cs+ for K+ in the internal solution. The outward K+ current had two major components: a fast tetraethylammonium (TEA)-insensitive, voltage dependent I(A)-type current which showed voltage dependent inactivation; and a TEA sensitive current which had characteristics of a calcium dependent IK(Ca)-type current. Transient changes (20 ms duration) in membrane potential mimicking that which could be produced by the transduction current during cilial displacement potently modulated the I(A) current. Depolarizing current pulses of greater than 63800 pA were required to elicit membrane voltage oscillations. The resulting membrane potential offset of at least 40 mV is well beyond the magnitude of hair cell receptor potentials making it unlikely that these oscillations would play a role in enhancing frequency selectivity.(ABSTRACT TRUNCATED AT 400 WORDS)
从青蛙（豹蛙）壶腹嵴分离出的毛细胞可存活长达5小时，并使用全细胞膜电压钳和电流钳记录进行研究。将分离出的壶腹嵴毛细胞的形态特征与通过光学显微镜和电子显微镜原位研究的毛细胞进行比较。虽然其他内耳毛细胞，如哺乳动物耳蜗的内、外毛细胞、青蛙球囊毛细胞和海龟耳蜗毛细胞通常呈圆柱形，但青蛙的壶腹嵴毛细胞主要呈球根状，有一个细长的细干从刚好能容纳细胞核的球形基部伸出。这种形状与在组织学材料中原位观察到的壶腹嵴毛细胞的紧密排列结构很好地相关。支持细胞常常不能分隔相邻的毛细胞，尤其是毛细胞的顶端。感觉上皮嵴上的最大细胞密度似乎是通过这种排列实现的。分离出的壶腹嵴毛细胞的平均静息膜电位（Vz）为-44.8 mV。表面光滑且明显不透明的细胞具有最负的Vz电位。随着细胞似乎开始退化，会出现透明度增加和细胞表面颗粒化。这样的细胞具有更正向的初始Vz值。Vz值比-15 mV更正的细胞表现出明显的、轮廓清晰的细胞核。缺乏这些退化指标的细胞的特征是输入电阻为1.9±0.31 GΩ，膜时间常数为13±2.5 ms。鉴定出一种大的复合外向整流电流，当用Cs⁺替代内部溶液中的K⁺时，该电流被消除。外向K⁺电流有两个主要成分：一种快速的四乙铵（TEA）不敏感、电压依赖性的I(A)型电流，表现出电压依赖性失活；以及一种TEA敏感电流，具有钙依赖性IK(Ca)型电流的特征。模拟纤毛位移期间转导电流可能产生的膜电位瞬变（持续20毫秒）有力地调节了I(A)电流。大于63800 pA的去极化电流脉冲才能引发膜电压振荡。由此产生的至少40 mV的膜电位偏移远远超过毛细胞受体电位的幅度，这使得这些振荡不太可能在增强频率选择性方面发挥作用。（摘要截断于400字）
