VARIATION OF MEMBRANE-PROPERTIES IN HAIR-CELLS ISOLATED FROM THE TURTLE COCHLEA
VARIATION OF MEMBRANE-PROPERTIES IN HAIR-CELLS ISOLATED FROM THE TURTLE COCHLEA
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DOI：
10.1113/jphysiol.1987.sp016492
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发表时间：
1987-04-01
影响因子：
5.5
通讯作者：
FETTIPLACE, R
中科院分区：
文献类型：
--
作者：
ART, JJ;FETTIPLACE, R
从龟基底乳头的确定区域酶法分离毛细胞，并与贴片电极技术进行了研究。实验的目的是将在电流注入过程中观察到的共振特性与在全细胞电压钳下在同一细胞中测量的膜电流相关联。孤立毛细胞的静息电位约为-50 mV，在小电流阶跃的开始和终止时产生膜电位的阻尼振荡;细胞之间的共振频率从9 Hz到350 Hz不等，并且与细胞分离的乳头区域相关。推断的频率图与先前在完整的乳头中描述的音调排列一致。电压钳下的测试电位的去极化激活了一个大的净外向电流与陡峭的电压依赖性，和稳态的电流-电压关系被强烈整流约静息电位。在具有较高谐振频率的细胞中，输入电阻往往较小，但从细胞电容推断，膜面积没有同时变化。通过细胞外应用25 mM-四乙基氯化铵（TEA）或在填充记录电极的细胞内介质中将Cs+交换为K+，消除了外向电流，每个实验都支持K+是主要电流载体的论点。这种治疗也消除了由施加的电流阶跃引起的膜电位振荡。此外，TEA或细胞内灌注Cs+也揭示了一个快速的内向电流的离子敏感性与其被携带的Ca 2+。像K+电流一样，Ca 2+电流也是由静息电位的小去极化激活的，在这个电压范围内，它比K+电流小大约5到10倍。它的激活比高频细胞中最快的外向电流更快。内向电流也可以由Ba ~（2+）携带，当Ba ~（2+）替代外部Ca ~（2+）时，K ~+电流被阻断。对共振频率为13-240 Hz的电池的测量表明，峰值Ba 2+电流随共振频率系统地增加。预期可减少或消除Ca 2+电流的操作（如外部添加Cd 2+）也可阻断K+电流，这与先前的建议（刘易斯and Hudspeth，1983 b）一致，即毛细胞K+电导受细胞内Ca 2+变化门控。结果支持以下结论：（i）耳蜗毛细胞的共振行为和调谐受膜Ca ~（2+）和K ~+电导的相互作用控制，（ii）共振频率由K ~+电导的特性决定，频率的增加主要是通过更快的动力学实现的，但在某种程度上也是通过电导的大小的增加实现的;（iii）Ca 2+电导的大小随着共振频率而增加，这可能需要增强调谐的锐度;（iv）膜特性随着沿沿着基底乳头的距离单调地分级。
Hair cells were enzymatically isolated from identified regions of the turtle basilar papilla and studied with the patch-electrode technique. The experimental aim was to relate the resonance properties seen during current injection to the membrane currents measured in the same cell under whole-cell voltage clamp. Solitary hair cells had resting potentials of about -50 mV, and produced a damped oscillation in membrane potential at the onset and termination of a small current step; the resonant frequency varied from 9 to 350 Hz between cells, and was correlated with the region of papilla from which a cell had been isolated. The inferred frequency map was consistent with the tonotopic arrangement described previously in the intact papilla. Depolarizations from the testing potential under voltage clamp activated a large net outward current with a steep voltage dependence, and the steady-state current-voltage relationship was strongly rectified about the resting potential. Input resistances tended to be smaller in cells with higher resonant frequencies, although there was not concurrent variation in membrane area as inferred from the cell capacitance. The outward current abolished by extracellular application of 25 mM-tetraethylammonium chloride (TEA), or on exchange of Cs+ for K+ in the intracellular medium filling the recording electrode, each experiment supporting the contention that K+ is the major current carrier. Such treatments also removed the oscillations in membrane potential evoked by imposed current steps. Addition of TEA or intracellular perfusion with Cs+ also revealed a fast inward current with an ionic sensitivity consistent with its being carried by Ca2+. Like the K+ current, the Ca2+ current was activated by small depolarizations from the resting potential, and over this voltage range it was about five to ten times smaller than the K+ current. Its activation was more rapid than the fastest outward currents in high-frequency cells. The inward current could also be carried by Ba2+, which when substituted for external Ca2+ blocked the K+ current. Measurements on cells with resonant frequencies of 13-240 Hz indicated that the peak Ba2+ current increased systematically with resonant frequency. Manipulations such as external addition of Cd2+ which would be expected to reduce or abolish the Ca2+ current also blocked the K+ current, consistent with a previous suggestion (Lewis and Hudspeth, 1983b) that the hair-cell K+ conductance is gated by changes in intracellular Ca2+. The results support the following conclusions: (i) the resonance behaviour and tuning of turtle cochlear hair cells are governed by the interplay of membrane Ca2+ and K+ conductances; (ii) the resonant frequency is determined by the characteristics of the K+ conductance, an increase in frequency being achieved largely by faster kinetics, but also to some extent by an increase in the size of this conductance; (iii) the magnitude of the Ca2+ conductance increases with resonant frequency and this may be needed to enhance the sharpness of tuning; (iv) the membrane properties are graded monotonically with distance along the basilar papilla.