Muñoz D J, Kendrick I S, Rassam M, Thorne P R
Discipline of Audiology, Division of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand.
Acta Otolaryngol. 2001 Jan;121(1):10-5. doi: 10.1080/000164801300006209.
Previous studies have revealed putative vesicular stores of adenosine triphosphate (ATP) in the marginal cells of the cochlear stria vascularis which may serve as a source of ATP for purinergic signalling. This study aimed to provide further evidence of ATP storage in the cochlea and to see whether ATP levels in the endolymph are affected by noise and hypoxia. Tissues from the lateral wall and organ of Corti of the guinea-pig cochlea were fractionated to obtain vesicular (VF) and mitochondrial (MF) fractions. Free and total ATP were then measured by the luciferase-luciferin reaction from which membrane-bound vesicular ATP was calculated. In the lateral wall, the VF contained 2.02+/-0.04 nmol ATP/mg protein (n = 5), significantly greater (p < 0.001; paired Student's t-test) than the concentration of ATP in the MF (0.36+/-0.05). In the organ of Corti, the VF contained 0.69+/-0.08 nmol ATP/mg protein (n = 4), significantly smaller than the amount in the VF of the lateral wall tissues (p < 0.001; non-paired Student's t-test). Small amounts of fumarase. an enzyme of the mitochondrial matrix, in the VF, excluded the possibility of mitochondrial ATP contamination. To investigate the effect of hypoxia and noise on the ATP concentrations in the endolymph, fluid samples were collected from the first (basal) cochlear turn of anaesthetized guinea-pigs. As a result of hypoxia (15 min, 13% F1O2), ATP concentrations (nM, mean +/- SEM) increased from 6.2+/-2.3 to 9.3+/-4.5 (n = 4), but the difference was not statistically significant. As a result of noise (15 min, 10 kHz, 110 dB SPL. broad band), the ATP levels increased significantly from 7.4+/-1.2 to 16.0+/-1.8 (p = 0.01; Student's t-test: n = 4). This study has demonstrated the presence of a vesicular store of ATP in the stria vascularis of the cochlea and described an increase in the ATP levels in the endolymph during noise exposure. The findings suggest that ATP is actively secreted from the vesicular store under conditions of metabolic stress. The presence of ATP under basal conditions supports a role for ATP in the sound transduction process during normal function.
先前的研究表明，耳蜗血管纹边缘细胞中存在假定的三磷酸腺苷（ATP）囊泡储存，这可能是嘌呤能信号传导的ATP来源。本研究旨在为耳蜗中ATP的储存提供进一步证据，并观察内淋巴中的ATP水平是否受噪声和缺氧影响。对豚鼠耳蜗外侧壁和柯蒂氏器的组织进行分级分离，以获得囊泡（VF）和线粒体（MF）组分。然后通过荧光素酶-荧光素反应测量游离ATP和总ATP，由此计算膜结合的囊泡ATP。在外侧壁中，VF中含有2.02±0.04 nmol ATP/mg蛋白质（n = 5），显著高于（p < 0.001；配对学生t检验）MF中的ATP浓度（0.36±0.05）。在柯蒂氏器中，VF含有0.69±0.08 nmol ATP/mg蛋白质（n = 4），显著低于外侧壁组织VF中的含量（p < 0.001；非配对学生t检验）。VF中存在少量线粒体基质酶富马酸酶，排除了线粒体ATP污染的可能性。为了研究缺氧和噪声对内淋巴中ATP浓度的影响，从麻醉豚鼠的耳蜗第一（基底）转收集液体样本。缺氧（15分钟，13% F1O2）后，ATP浓度（nM，平均值±标准误）从6.2±2.3增加到9.3±4.5（n = 4），但差异无统计学意义。噪声（15分钟，10 kHz，110 dB SPL，宽带）后，ATP水平从7.4±1.2显著增加到16.0±1.8（p = 0.01；学生t检验：n = 4）。本研究证明了耳蜗血管纹中存在ATP囊泡储存，并描述了噪声暴露期间内淋巴中ATP水平的增加。研究结果表明，在代谢应激条件下，ATP从囊泡储存中被主动分泌。基础条件下ATP的存在支持了ATP在正常功能的声音传导过程中的作用。
