Department of Physiology, University of Arizona, P.O. Box 245051, Tucson, AZ 85724, USA.
Int J Mol Sci. 2018 Jun 4;19(6):1659. doi: 10.3390/ijms19061659.
Connexin 43 (Cx43), a gap junction protein seemingly fit to support cardiac impulse propagation and synchronic contraction, is phosphorylated in normoxia by casein kinase 1 (CK1). However, during cardiac ischemia or pressure overload hypertrophy, this phosphorylation fades, Cx43 abundance decreases at intercalated disks and increases at myocytes' lateral borders, and the risk of arrhythmia rises. Studies in wild-type and transgenic mice indicate that enhanced CK1-phosphorylation of Cx43 protects from arrhythmia, while dephosphorylation precedes arrhythmia vulnerability. The mechanistic bases of these Cx43 (de)phosphoform-linked cardiac phenotypes are unknown. We used patch-clamp and dye injection techniques to study the channel function (gating, permeability) of Cx43 mutants wherein CK1-targeted serines were replaced by aspartate (Cx43-CK1-D) or alanine (Cx43-CK1-A) to emulate phosphorylation and dephosphorylation, respectively. Cx43-CK1-D, but not Cx43-CK1-A, displayed high Voltage-sensitivity and variable permselectivity. Both mutants showed multiple channel open states with overall increased conductivity, resistance to acidification-induced junctional uncoupling, and hemichannel openings in normal external calcium. Modest differences in the mutant channels' function and regulation imply the involvement of dissimilar structural conformations of the interacting domains of Cx43 in electrical and chemical gating that may contribute to the divergent phenotypes of CK1-(de)phospho-mimicking Cx43 transgenic mice and that may bear significance in arrhythmogenesis.
间隙连接蛋白 43（Cx43）似乎适合支持心脏冲动的传播和同步收缩，在常氧条件下通过酪蛋白激酶 1（CK1）磷酸化。然而，在心脏缺血或压力超负荷肥大期间，这种磷酸化消失，Cx43 在闰盘处的丰度降低，在心肌细胞的侧边界处增加，心律失常的风险增加。野生型和转基因小鼠的研究表明，增强的 Cx43 的 CK1 磷酸化可保护免受心律失常，而去磷酸化先于心律失常易感性。这些 Cx43（去）磷酸化形式相关的心脏表型的机制基础尚不清楚。我们使用膜片钳和染料注射技术研究了 Cx43 突变体的通道功能（门控、通透性），其中 CK1 靶向丝氨酸被天冬氨酸（Cx43-CK1-D）或丙氨酸（Cx43-CK1-A）取代，分别模拟磷酸化和去磷酸化。Cx43-CK1-D，但不是 Cx43-CK1-A，显示出高电压敏感性和可变的选择性。两种突变体均显示出多个通道开放状态，整体导电性增加，对酸化诱导的连接解偶联的抗性增强，以及正常外钙中的半通道开放。突变体通道功能和调节的微小差异表明，Cx43 的相互作用域的不同结构构象参与了电和化学门控，这可能导致 CK1-（去）磷酸化模拟 Cx43 转基因小鼠的不同表型，并可能在心律失常发生中具有重要意义。
