The mechanism underlying maintenance of the endocochlear potential by the K+ transport system in fibrocytes of the inner ear
The mechanism underlying maintenance of the endocochlear potential by the K+ transport system in fibrocytes of the inner ear
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DOI：
10.1113/jphysiol.2013.258046
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发表时间：
2013-09-15
影响因子：
5.5
通讯作者：
Kurachi, Yoshihisa
中科院分区：
文献类型：
--
作者：
Adachi, Naoko;Yoshida, Takamasa;Kurachi, Yoshihisa
内淋巴电位（EP）为+80毫伏，存在于蜗管中，它对于听觉至关重要，其受钾离子（K⁺）跨蜗管外侧壁的转运调控。蜗管外侧壁包含两个上皮屏障，即合胞体和边缘细胞。前者包含多种细胞类型，如纤维细胞，其基底外侧表面暴露于外淋巴。边缘细胞的顶端表面面向内淋巴。在这两个屏障之间是间隙（IS），这是一个细胞外间隙，钾离子浓度（[K⁺]）较低，且电位与内淋巴电位相似。这种间隙电位（ISP）主导内淋巴电位，它代表了由合胞体顶端表面较大的钾离子浓度梯度引发的扩散电位与合胞体电位之和，合胞体电位相对于外淋巴略呈正值。尽管纤维细胞中的钾离子转运系统似乎对内淋巴电位有贡献，但其机制仍不明确。我们使用对电位和钾离子敏感的电极，在向鼓阶外淋巴灌注钠钾 - 腺苷三磷酸酶（Na⁺,K⁺ - ATP酶，被认为是该系统关键的钾离子泵）阻断剂的同时，检测豚鼠蜗管外侧壁的电化学特性。抑制钠钾 - 腺苷三磷酸酶对间隙中的[K⁺]几乎没有影响，但却大幅降低了合胞体内的[K⁺]，减小了其顶端表面的钾离子浓度梯度。该处理仅适度使合胞体超极化。结果，间隙电位和内淋巴电位均下降。显然，纤维细胞利用钠钾 - 腺苷三磷酸酶实现局部钾离子转运，维持合胞体较高的[K⁺]，这对于形成正间隙电位的钾离子扩散过程至关重要。
The endocochlear potential (EP) of +80 mV in the scala media, which is indispensable for audition, is controlled by K+ transport across the lateral cochlear wall. This wall includes two epithelial barriers, the syncytium and the marginal cells. The former contains multiple cell types, such as fibrocytes, which are exposed to perilymph on their basolateral surfaces. The apical surfaces of the marginal cells face endolymph. Between the two barriers lies the intrastrial space (IS), an extracellular space with a low K+ concentration ([K+]) and a potential similar to the EP. This intrastrial potential (ISP) dominates the EP and represents the sum of the diffusion potential elicited by a large K+ gradient across the apical surface of the syncytium and the syncytium's potential, which is slightly positive relative to perilymph. Although a K+ transport system in fibrocytes seems to contribute to the EP, the mechanism remains uncertain. We examined the electrochemical properties of the lateral wall of guinea pigs with electrodes sensitive to potential and K+ while perfusing into the perilymph of the scala tympani blockers of Na+,K+-ATPase, the K+ pump thought to be essential to the system. Inhibiting Na+,K+-ATPase barely affected [K+] in the IS but greatly decreased [K+] within the syncytium, reducing the K+ gradient across its apical surface. The treatment hyperpolarized the syncytium only moderately. Consequently, both the ISP and the EP declined. Fibrocytes evidently use the Na+,K+-ATPase to achieve local K+ transport, maintaining the syncytium's high [K+] that is crucial for the K+ diffusion underlying the positive ISP.