Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, 194064 St. Petersburg, Russia.
Int J Mol Sci. 2021 Apr 30;22(9):4767. doi: 10.3390/ijms22094767.
Microdomains formed by proteins of endoplasmic reticulum and plasma membrane play a key role in store-operated Ca entry (SOCE). Ca release through inositol 1,4,5-trisphosphate receptor (IPR) and subsequent Ca store depletion activate STIM (stromal interaction molecules) proteins, sensors of intraluminal Ca, which, in turn, open the Orai channels in plasma membrane. Downstream to this process could be activated TRPC (transient receptor potential-canonical) calcium permeable channels. Using single channel patch-clamp technique we found that a local Ca entry through TRPC1 channels activated endogenous Ca-activated chloride channels (CaCCs) with properties similar to Anoctamin6 (TMEM16F). Our data suggest that their outward rectification is based on the dependence from membrane potential of both the channel conductance and the channel activity: (1) The conductance of active CaCCs highly depends on the transmembrane potential (from 3 pS at negative potentials till 60 pS at positive potentials); (2) their activity (NPo) is enhanced with increasing Ca concentration and/or transmembrane potential, conversely lowering of intracellular Ca concentration reduced the open state dwell time; (3) CaCC amplitude is only slightly increased by intracellular Ca concentration. Experiments with Ca buffering by EGTA or BAPTA suggest close local arrangement of functional CaCCs and TRPC1 channels. It is supposed that Ca-activated chloride channels are involved in Ca entry microdomains.
内质网和质膜蛋白形成的微域在钙库操纵性钙内流（SOCE）中发挥关键作用。通过肌醇 1,4,5-三磷酸受体（IPR）释放 Ca 和随后的 Ca 储存耗竭激活 STIM（基质相互作用分子）蛋白，作为腔内 Ca 的传感器，反过来又打开质膜中的 Orai 通道。在此过程的下游，可能会激活瞬时受体电位经典型（TRPC）钙通透通道。使用单通道膜片钳技术，我们发现 TRPC1 通道通过局部 Ca 内流激活具有类似于 Anoctamin6（TMEM16F）特性的内源性 Ca 激活氯离子通道（CaCC）。我们的数据表明，它们的外向整流基于通道电导和通道活性对膜电位的依赖性：（1）活性 CaCC 的电导高度依赖于跨膜电位（从负电位的 3 pS 到正电位的 60 pS）；（2）它们的活性（NPo）随着 Ca 浓度和/或跨膜电位的增加而增强，相反，细胞内 Ca 浓度的降低会减少开放状态停留时间；（3）细胞内 Ca 浓度的增加仅略微增加 CaCC 的幅度。用 EGTA 或 BAPTA 进行的 Ca 缓冲实验表明，功能性 CaCC 和 TRPC1 通道之间存在紧密的局部排列。据推测，Ca 激活的氯离子通道参与 Ca 内流微域。
