Kim Woo Bin, Kang Kwon-Woo, Sharma Kushal, Yi Eunyoung
College of Pharmacy and Natural Medicine Research Institute, Mokpo National University, Muan 58554, Korea.
Exp Neurobiol. 2020 Oct 31;29(5):344-355. doi: 10.5607/en20043.
K3 family K channels, by ensuring speedy repolarization of action potential, enable rapid and high frequency neuronal firing and high precision temporal coding of auditory information in various auditory synapses in the brain. Expression of different K3 subtypes within the auditory end organ has been reported. Yet, their precise role at the hair cell synaptic transmission has not been fully elucidated. Using immunolabeling and confocal microscopy we examined the expression pattern of different K3 family K channel subunits in the nerve fibers innervating the cochlear hair cells. K3.1b was found in NKA-positive type 1 afferent fibers, exhibiting high signal intensity at the cell body, the unmyelinated dendritic segment, first heminode and nodes of Ranvier. K3.3 signal was detected in the cell body and the unmyelinated dendritic segment of NKA-positive type 1 afferent fibers but not in peripherin-positive type 2 afferent. K3.4 was found in ChAT-positive LOC and MOC efferent fibers as well as peripherin-positive type 2 afferent fibers. Such segregated expression pattern implies that each K3 subunits participate in different auditory tasks, for example, K3.1b and K3.3 in ascending signaling while K3.4 in feedback upon loud noise exposure.
K3家族钾通道通过确保动作电位的快速复极化，使得大脑中各种听觉突触能够实现快速且高频的神经元放电以及对听觉信息进行高精度的时间编码。已有报道称在听觉终器内存在不同的K3亚型表达。然而，它们在毛细胞突触传递中的精确作用尚未完全阐明。我们利用免疫标记和共聚焦显微镜检查了支配耳蜗毛细胞的神经纤维中不同K3家族钾通道亚基的表达模式。发现K3.1b存在于NKA阳性的I型传入纤维中，在细胞体、无髓树突段、第一半结和郎飞结处表现出高信号强度。在NKA阳性的I型传入纤维的细胞体和无髓树突段检测到K3.3信号，但在外周蛋白阳性的II型传入纤维中未检测到。在ChAT阳性的外侧橄榄耳蜗束和内侧橄榄耳蜗束传出纤维以及外周蛋白阳性的II型传入纤维中发现了K3.4。这种分离的表达模式意味着每个K3亚基参与不同的听觉任务，例如，K3.1b和K3.3参与上行信号传导，而K3.4在噪声暴露后的反馈中起作用。
