Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV, USA.
Present address: Division of Gastroenterology and Hepatology, Department of Internal Medicine, Yeungnam University College of Medicine, Nam-Gu, Daegu, South Korea.
J Physiol. 2018 Feb 1;596(3):379-391. doi: 10.1113/JP275234. Epub 2017 Dec 27.
Interstitial cells of Cajal (ICC) from murine colonic muscles express genes encoding inwardly rectifying K channels. Transcripts of Kcnj2 (Kir2.1), Kcnj4 (Kir2.3), Kcnj14 (Kir2.4), Kcnj5 (Kir3.4), Kcnj8 (Kir 6.1) and Kcnj11 (Kir6.2) were found in colonic ICC. A conductance with properties consistent with Kir2 channels was observed in ICC but not in smooth muscle cells (SMC). Despite expression of gene transcripts, G-protein gated K channel (Kir3) and K (Kir6) currents were not resolved in ICC. K is a conductance prominent in SMC. Kir2 antagonist caused depolarization of freshly dispersed ICC and colonic smooth muscles, suggesting that this conductance is active under resting conditions in colonic muscles. The conclusion of the present study is that ICC express the Ba -sensitive, inwardly rectifying K conductance in colonic muscles. This conductance is most probably a result of heterotetramers of Kir2 gene products, with this regulating resting potentials and the excitability of colonic muscles.
Membrane potentials of gastrointestinal muscles are important because voltage-dependent Ca channels in smooth muscle cells (SMC) provide the Ca that triggers contraction. Regulation of membrane potential is complicated because SMC are electrically coupled to interstitial cells of Cajal (ICC) and PDGFRα cells. Activation of conductances in any of these cells affects the excitability of the syncytium. We explored the role of inward rectifier K conductances in colonic ICC that might contribute to regulation of membrane potential. ICC expressed Kcnj2 (Kir2.1), Kcnj4 (Kir2.3), Kcnj14 (Kir2.4), Kcnj5 (Kir3.4), Kcnj8 (Kir 6.1) and Kcnj11 (Kir6.2). Voltage clamp experiments showed activation of inward current when extracellular K ([K ] ) was increased. The current was inwardly rectifying and inhibited by Ba (10 μm) and ML-133 (10 μm). A similar current was not available in SMC. The current activated in ICC by elevated [K ] was not affected by Tertiapin-Q. Gβγ, when dialysed into cells, failed to activate a unique, Tertiapin-Q-sensitive conductance. Freshly dispersed ICC showed no evidence of functional K . Pinacidil failed to activate current and the inward current activated by elevated [K ] was insensitive to glibenclamide. Under current clamp, ML-133 caused the depolarization of isolated ICC and also that of cells impaled with microelectrodes in intact muscle strips. These findings show that ICC, when isolated freshly from colonic muscles, expressed a Ba -sensitive, inwardly rectifying K conductance. This conductance is most probably a result of the expression of multiple Kir2 family paralogues, and the inwardly rectifying conductance contributes to the regulation of resting potentials and excitability of colonic muscles.
来自鼠结直肠肌的 Cajal 间质细胞表达编码内向整流钾通道的基因。在结直肠 ICC 中发现了 Kcnj2（Kir2.1）、Kcnj4（Kir2.3）、Kcnj14（Kir2.4）、Kcnj5（Kir3.4）、Kcnj8（Kir 6.1）和 Kcnj11（Kir6.2）的转录本。在 ICC 中观察到具有与 Kir2 通道一致特性的电导，但在平滑肌细胞（SMC）中没有观察到。尽管存在基因转录本，但在 ICC 中没有解决 G 蛋白门控钾通道（Kir3）和 K（Kir6）电流。K 是 SMC 中突出的电导。Kir2 拮抗剂导致新鲜分散的 ICC 和结肠平滑肌去极化，表明在结肠肌肉的静息状态下，这种电导是活跃的。本研究的结论是，ICC 在结肠肌肉中表达 Ba 敏感的内向整流钾电导。这种电导很可能是 Kir2 基因产物的异四聚体的结果，这种电导调节着结肠肌肉的静息电位和兴奋性。
胃肠道肌肉的膜电位很重要，因为平滑肌细胞中的电压依赖性钙通道提供触发收缩的 Ca。膜电位的调节很复杂，因为 SMC 与 Cajal 间质细胞（ICC）和 PDGFRα 细胞电耦联。这些细胞中任何一种电导的激活都会影响同步细胞的兴奋性。我们探讨了内向整流钾电导在可能有助于调节膜电位的结直肠 ICC 中的作用。ICC 表达 Kcnj2（Kir2.1）、Kcnj4（Kir2.3）、Kcnj14（Kir2.4）、Kcnj5（Kir3.4）、Kcnj8（Kir 6.1）和 Kcnj11（Kir6.2）。当细胞外 K（[K]）增加时，电压钳实验显示内向电流的激活。该电流具有内向整流性，被 Ba（10μm）和 ML-133（10μm）抑制。SMC 中没有类似的电流。由升高的[K]激活的 ICC 中的电流不受 Tertiapin-Q 的影响。当 Gβγ 被透析到细胞中时，未能激活独特的、Tertiapin-Q 敏感的电导。新鲜分散的 ICC 没有显示出功能性 K 的证据。Pinacidil 未能激活电流，而由升高的[K]激活的内向电流对格列本脲不敏感。在电流钳下，ML-133 导致分离的 ICC 去极化，也导致完整肌肉条中用微电极刺穿的细胞去极化。这些发现表明，从结直肠肌肉中新鲜分离的 ICC 表达了 Ba 敏感的内向整流钾电导。这种电导很可能是多种 Kir2 家族同源物表达的结果，内向整流电导有助于调节结直肠肌肉的静息电位和兴奋性。
