Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Healthy Aging Research Center, Chang Gung University, Taoyuan, Taiwan; Neuroscience Research Center, Chang Gung Memorial Hospital at Linkou, Taoyuan, Taiwan.
Biomed J. 2023 Aug;46(4):100551. doi: 10.1016/j.bj.2022.07.005. Epub 2022 Jul 19.
Intercellular coupling is essential for the suprachiasmatic nucleus (SCN) to serve as a coherent central clock. Synaptic release of neurotransmitters and neuropeptides is critical for synchronizing SCN neurons. However, intercellular coupling via non-synaptic mechanisms has also been demonstrated. In particular, the abundant perikaryal appositions with morphological specializations in the narrow extracellular space (ECS) may hinder molecular diffusion to allow for ion accumulation or depletion.
The SCN neurons were recorded in the whole-cell current-clamp mode, with pipette filled with high (26 mM)-Na or low (6 mM)-Na solution.
Cells recorded with high-Na pipette solution could fire spontaneous action potentials (AP) with peak AHP more negative than the calculated value of K equilibrium potential (E) and with peak AP more positive than calculated E. Cells recorded with low-Na pipette solution could also have peak AHP more negative than calculated E. In contrast, the resting membrane potential (RMP) was always less negative to calculated E. The distribution and the averaged amplitude of peak AHP, peak AP, or RMP was similar between cells recorded with high-Na and low-Na solution pipette. In a number of cells, the peak AHP could increase from more positive to become more negative than calculated E spontaneously or after treatments to hyperpolarize the RMP. TTX blocked the Na -dependent APs and tetraethylammonium (TEA), but not Ba or Cd, markedly reduced the peak AHP. Perforated-patch cells could also but rarely fire APs with peak AHP more negative than calculated E.
The result of peak AHP negative to calculated E indicates that local [K] sensed by the TEA-sensitive AHP K channels must be lower than bulk [K], most likely due to K clearance from K diffusion-restricted ECS by the Na/K-ATPase. The K diffusion-restricted ECS may allow for K-mediated ionic interactions among neurons to regulate SCN excitability.
细胞间耦联对于视交叉上核（SCN）作为一个协调的中央时钟是必不可少的。神经递质和神经肽的突触释放对于 SCN 神经元的同步至关重要。然而，通过非突触机制的细胞间耦联也已经得到证实。特别是，在狭窄的细胞外空间（ECS）中存在大量具有形态特化的胞体旁置，这可能会阻碍分子扩散，从而允许离子积累或耗尽。
SCN 神经元在全细胞电流钳模式下记录，用充满高（26 mM）-Na 或低（6 mM）-Na 溶液的玻璃微电极记录。
用高 Na 溶液灌流的玻璃微电极记录的细胞可以自发产生动作电位（AP），其峰 AHP 比计算的 K 平衡电位（E）更负，峰 AP 比计算的 E 更正。用低 Na 溶液灌流的玻璃微电极记录的细胞也可以有比计算的 E 更负的峰 AHP。相比之下，静息膜电位（RMP）总是比计算的 E 更正。用高 Na 和低 Na 溶液灌流的玻璃微电极记录的细胞的峰 AHP、峰 AP 或 RMP 的分布和平均幅度相似。在许多细胞中，峰 AHP 可以自发地或在处理后使 RMP 超极化而从更正变为更负，超过计算的 E。TTX 阻断了 Na 依赖性 AP，而四乙铵（TEA），但不是 Ba 或 Cd，显著降低了峰 AHP。穿孔膜片钳细胞也可以但很少产生峰 AHP 比计算的 E 更负的 AP。
峰 AHP 负于计算的 E 的结果表明，TEA 敏感的 AHP K 通道感知的局部[K]必须低于总体[K]，最有可能是由于 K 通过 Na/K-ATPase 从 K 扩散受限的 ECS 中清除。K 扩散受限的 ECS 可能允许神经元之间的 K 介导的离子相互作用来调节 SCN 的兴奋性。
