Department of Physiology and the Key Laboratory of Cellular Physiology, Ministry of Education, Shanxi Medical University, Taiyuan 030001, China.
Sci China Life Sci. 2013 Sep;56(9):788-96. doi: 10.1007/s11427-013-4531-z. Epub 2013 Aug 8.
We recently reported that zacopride is a selective inward rectifier potassium current (I K1) channel agonist, suppressing ventricular arrhythmias without affecting atrial arrhythmias. The present study aimed to investigate the unique pharmacological properties of zacopride. The whole-cell patch-clamp technique was used to study I K1 currents in rat atrial myocytes and Kir2.x currents in human embryonic kidney (HEK)-293 cells transfected with inward rectifier potassium channel (Kir)2.1, Kir2.2, Kir2.3, or mutated Kir2.1 (at phosphorylation site S425L). Western immunoblots were performed to estimate the relative protein expression levels of Kir2.x in rat atria and ventricles. Results showed that zacopride did not affect the IK1 and transmembrane potential of atrial myocytes. In HEK293 cells, zacopride increased Kir2.1 homomeric channels by 40.7%±9.7% at -50 mV, but did not affect Kir2.2 and Kir2.3 homomeric channels, and Kir2.1-Kir2.2, Kir2.1-Kir2.3 and Kir2.2-Kir2.3 heteromeric channels. Western immunoblots showed that similar levels of Kir2.3 protein were expressed in rat atria and ventricles, but atrial Kir2.1 protein level was only 25% of that measured in the ventricle. In addition, 5-hydroxytryptamine (5-HT)3 receptor was undetectable, whereas 5-HT4 receptor was weakly expressed in HEK293 cells. The Kir2.1-activating effect of zacopride in these cells was abolished by inhibition of protein kinase A (PKA), but not PKC or PKG. Furthermore, zacopride did not activate the mutant Kir2.1 channel in HEK293 cells but selectively activated the Kir2.1 homomeric channel via a PKA-dependent pathway, independent to that of the 5-HT receptor.
我们最近报道扎考必利是一种选择性内向整流钾电流（I K1）通道激动剂，可抑制室性心律失常而不影响房性心律失常。本研究旨在探讨扎考必利的独特药理学特性。使用全细胞膜片钳技术研究大鼠心房肌细胞中的 I K1 电流和转染内向整流钾通道（Kir）2.1、Kir2.2、Kir2.3 或突变 Kir2.1（在磷酸化位点 S425L）的人胚肾（HEK）-293 细胞中的 Kir2.x 电流。Western 免疫印迹用于估计大鼠心房和心室中 Kir2.x 的相对蛋白表达水平。结果表明，扎考必利不影响心房肌细胞的 IK1 和跨膜电位。在 HEK293 细胞中，扎考必利在-50 mV 时使 Kir2.1 同源通道增加 40.7%±9.7%，但不影响 Kir2.2 和 Kir2.3 同源通道，以及 Kir2.1-Kir2.2、Kir2.1-Kir2.3 和 Kir2.2-Kir2.3 异源通道。Western 免疫印迹显示，大鼠心房和心室中表达的 Kir2.3 蛋白水平相似，但心房 Kir2.1 蛋白水平仅为心室的 25%。此外，5-羟色胺（5-HT）3 受体无法检测到，而 5-HT4 受体在 HEK293 细胞中表达较弱。PKA 抑制可消除扎考必利对这些细胞中 Kir2.1 通道的激活作用，但不能消除 PKC 或 PKG。此外，扎考必利不能激活 HEK293 细胞中的突变 Kir2.1 通道，但通过 PKA 依赖性途径选择性激活 Kir2.1 同源通道，与 5-HT 受体无关。
