The currents of α7 nicotinic acetylcholine receptors activated by acetylcholine (ACh) are brief. The channel has high permeability to calcium relative to monovalent cations and shows inward rectification. It has been previously noted that in the presence of positive allosteric modulators (PAMs), currents through the channels of α7 receptors differ from normal α7 currents both in sensitivity to specific channel blockers and their current-voltage (I-V) relationships, no longer showing inward rectification. Linear I-V functions are often associated with channels lacking calcium permeability, so we measured the I-V functions of α7 receptors activated by ACh when PAMs were bound to the allosteric binding site in the transmembrane domain. Currents were recorded in chloride-free Ringer’s solution with low or high concentrations of extracellular calcium to determine the magnitude of the reversal potential shift in the two conditions as well as the I-V relationships. ACh-evoked currents potentiated by the allosteric agonist–PAMs (ago-PAMs) (3aR,4S,9bS)-4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide (GAT107) and 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propenamide (B-973B) showed reduced inward rectification and calcium-dependent reversal potential shifts decreased by 80%, and 50%, respectively, compared with currents activated by ACh alone, indicative of reduced calcium permeability. Currents potentiated by 3a,4,5,9b-tetrahydro-4-(1-naphthalenyl)-3H-cyclopentan[c]quinoline-8-sulfonamide were also linear and showed no calcium-dependent reversal potential shifts. The ago-PAMs GAT-107 and B-973B stimulated increases in intracellular calcium in stably transfected HEK293 cells. However, these calcium signals were delayed relative to channel activation produced by these agents and were insensitive to the channel blocker mecamylamine. Our results indicate that, although allosterically activated α7 nicotinic ACh receptor may affect intracellular calcium levels, such effects are not likely due to large channel-dependent calcium influx.

中文翻译：

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变构增强α7烟碱乙酰胆碱受体：降低钙渗透性和细胞内钙的电流独立控制

由乙酰胆碱 (ACh) 激活的α 7 烟碱型乙酰胆碱受体的电流很短。相对于单价阳离子，该通道对钙具有高渗透性，并显示出向内整流。之前已经注意到，在存在正变构调节剂 (PAM) 的情况下，通过α 7 受体通道的电流在对特定通道阻滞剂及其电流-电压 (IV) 关系的敏感性方面与正常α 7 电流不同，不再表现出内向的纠正。线性 IV 函数通常与缺乏钙渗透性的通道相关，因此我们测量了α的 IV 函数当 PAM 与跨膜结构域中的变构结合位点结合时，ACh 激活了 7 种受体。在具有低浓度或高浓度细胞外钙的无氯林格氏溶液中记录电流，以确定两种条件下逆转电位变化的幅度以及 IV 关系。由别构激动剂-PAMs (ago-PAMs) (3aR,4S,9bS)-4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-增强的乙酰胆碱诱发电流8-磺酰胺 (GAT107) 和 3-(3,4-二氟苯基) -N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propenamide (B-973B) 表现出减少的内向整流和钙依赖性逆转电位转移减少与单独由 ACh 激活的电流相比，分别为 80% 和 50%，表明钙渗透性降低。由 3a,4,5,9b-tetrahydro-4-(1-naphthalenyl)-3H-cyclopentan[c]quinoline-8-sulfonamide 增强的电流也是线性的，没有显示出与钙有关的逆转电位变化。在稳定转染的 HEK293 细胞中，ago-PAMs GAT-107 和 B-973B 刺激细胞内钙的增加。然而，这些钙信号相对于这些试剂产生的通道激活被延迟，并且对通道阻滞剂美加明不敏感。我们的结果表明，虽然变构激活的α7 烟碱型 ACh 受体可能会影响细胞内钙离子水平，这种影响不太可能是由于大量的通道依赖性钙离子流入。