Roongthumskul Yuttana, Faber Justin, Bozovic Dolores
Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
Department of Physics & Astronomy, University of California, Los Angeles, Los Angeles, California.
Biophys J. 2021 Jan 19;120(2):205-216. doi: 10.1016/j.bpj.2020.11.2273. Epub 2020 Dec 15.
The high sensitivity and effective frequency discrimination of sound detection performed by the auditory system rely on the dynamics of a system of hair cells. In the inner ear, these acoustic receptors are primarily attached to an overlying structure that provides mechanical coupling between the hair bundles. Although the dynamics of individual hair bundles has been extensively investigated, the influence of mechanical coupling on the motility of the system of bundles remains underdetermined. We developed a technique of mechanically coupling two active hair bundles, enabling us to probe the dynamics of the coupled system experimentally. We demonstrated that the coupling could enhance the coherence of hair bundles' spontaneous oscillation, as well as their phase-locked response to sinusoidal stimuli, at the calcium concentration in the surrounding fluid near the physiological level. The empirical data were consistent with numerical results from a model of two coupled nonisochronous oscillators, each displaying a supercritical Hopf bifurcation. The model revealed that a weak coupling can poise the system of unstable oscillators closer to the bifurcation by a shift in the critical point. In addition, the dynamics of strongly coupled oscillators far from criticality suggested that individual hair bundles may be regarded as nonisochronous oscillators. An optimal degree of nonisochronicity was required for the observed tuning behavior in the coherence of autonomous motion of the coupled system.
听觉系统执行的声音检测的高灵敏度和有效的频率辨别依赖于毛细胞系统的动力学。在内耳中，这些听觉感受器主要附着于一个覆盖结构，该结构在毛束之间提供机械耦合。尽管单个毛束的动力学已得到广泛研究，但机械耦合对毛束系统运动性的影响仍未完全确定。我们开发了一种机械耦合两个活性毛束的技术，使我们能够通过实验探究耦合系统的动力学。我们证明，在周围流体中的钙浓度接近生理水平时，这种耦合可以增强毛束自发振荡的相干性，以及它们对正弦刺激的锁相响应。实验数据与两个耦合的非等时振荡器模型的数值结果一致，每个振荡器都表现出超临界霍普夫分岔。该模型表明，弱耦合可以通过临界点的移动使不稳定振荡器系统更接近分岔点。此外，远离临界点的强耦合振荡器的动力学表明，单个毛束可被视为非等时振荡器。耦合系统自主运动相干性中观察到的调谐行为需要最佳程度的非等时性。
