Xu Ji, Nicholson Bruce J
Department of Pharmacology, Institute of Neuroscience, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou 450001, China.
Department of Biochemistry and Structural Biology, University of Texas Health at San Antonio, San Antonio, TX 78229, USA.
Life (Basel). 2023 Jan 31;13(2):390. doi: 10.3390/life13020390.
Cx30 has been proposed to play physiological functions in the kidney and cochlea, and this has often been associated with its hemichannel role (deafness mutants frequently affecting hemichannels more than gap junctions), implicated in ATP release. Here, we used heterologous expression systems ( and N2A cells) to describe the properties of Cx30 hemichannels, with the objective of better understanding their physiological functions. As previously observed, Cx30 hemichannels gated in response to transmembrane voltage (V) and extracellular [Ca] (pK[Ca] of 1.9 μM in the absence of Mg). They show minimal charge selectivity with respect to small ions (ratio of Na: K: Cl of 1: 0.4: 0.6) and an MW cut-off for Alexa Dyes between 643 (Alex 488) and 820 Da (Alexa 594). However, while cations follow the expected drop in conductance with size (Na to TEA is 1: 0.3), anions showed an increase, with a ratio of Cl to gluconate conductance of 1:1.4, suggesting favorable interactions between larger anions and the pore. This was further explored by comparing the permeabilities of both hemichannels and gap junctions to the natural anion (ATP), the release of which has been implicated in Ca signaling through hemichannels. We extended this analysis to two closely related connexins co-expressed in the cochlear, Cx26 and Cx30. Cx30 and 26 hemichannels displayed similar permeabilities to ATP, but surprisingly Cx26 gap junctions were six times more permeable than their hemichannels and four times more permeable than Cx30 gap junctions. This suggests a significant physiological difference in the functions of Cx26 and Cx30 gap junctions in organs where they are co-expressed, at least with regard to the distribution of energy resources of the cells. It also demonstrates that the permeability characteristics of hemichannels can significantly diverge from that of their gap junctions for some connexins but not others.
已有研究表明，Cx30在肾脏和耳蜗中发挥生理功能，这通常与其半通道作用有关（耳聋突变体对半通道的影响往往大于间隙连接），且与ATP释放有关。在此，我们使用异源表达系统（以及N2A细胞）来描述Cx30半通道的特性，目的是更好地理解其生理功能。如先前观察到的，Cx30半通道对跨膜电压（V）和细胞外[Ca]作出响应而门控（在无Mg时，pK[Ca]为1.9 μM）。它们对小离子的电荷选择性极小（Na:K:Cl的比率为1:0.4:0.6），对Alexa染料的分子量截止值在643（Alex 488）至820 Da（Alexa 594）之间。然而，虽然阳离子的电导率随尺寸的增加而如预期般下降（Na与TEA的比率为1:0.3），但阴离子的电导率却有所增加，Cl与葡萄糖酸盐的电导率比率为1:1.4，这表明较大的阴离子与孔之间存在有利的相互作用。通过比较半通道和间隙连接对天然阴离子（ATP）的通透性，进一步探究了这一现象，ATP的释放与通过半通道的Ca信号传导有关。我们将此分析扩展至在耳蜗中共表达的两种密切相关的连接蛋白Cx26和Cx30。Cx30和26半通道对ATP的通透性相似，但令人惊讶的是，Cx26间隙连接的通透性比其半通道高六倍，比Cx30间隙连接高四倍。这表明在它们共表达的器官中，Cx26和Cx30间隙连接的功能存在显著的生理差异，至少在细胞能量资源分布方面如此。这也表明，对于某些连接蛋白而言，半通道的通透性特征可能与其间隙连接的通透性特征有显著差异，而对于其他连接蛋白则不然。
