Guo Shuai, Chen Zhenhui, Chen Peng-Sheng, Rubart Michael
Division of Cardiology, Department of Medicine, The Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, IN, United States.
Department of Cardiology, Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States.
Front Pharmacol. 2021 Apr 22;12:651267. doi: 10.3389/fphar.2021.651267. eCollection 2021.
Small-conductance Ca-activated K channels (SK channels) have been proposed as antiarrhythmic targets for the treatment of atrial fibrillation. We previously demonstrated that the 5-HT receptor antagonist ondansetron inhibits heterologously expressed, human SK2 (hSK2) currents as well as native cardiac SK currents in a physiological extra-/intracellular [K] gradient at therapeutic (i.e., sub-micromolar) concentrations. A recent study, using symmetrical [K] conditions, challenged this result. The goal of the present study was to revisit the inhibitory effect of ondansetron on hSK2-mediated currents in symmetrical [K] conditions. The whole-cell patch clamp technique was used to investigate the effects of ondansetron and apamin on hSK2-mediated currents expressed in HEK 293 cells. Currents were measured in symmetrical [K] conditions in the presence of 100 nM [Ca]. Expression of hSK2 produced inwardly rectifying whole-cell currents in the presence of 400 nM free cytosolic Ca. Ondansetron inhibited whole-cell hSK2 currents with values of 154 and 113 nM at -80 and 40 mV, respectively. Macroscopic current inhibited by ondansetron and current inhibited by apamin exhibited inwardly rectifying current-voltage relationships with similar reversal potentials (apamin, ∼5 mV and ondansetron, ∼2 mV). Ondansetron (1 μM) in the continuing presence of apamin (100 nM) had no effect on hSK2-mediated whole-cell currents. Wild-type HEK 293 cells did not express ondansetron- or apamin-sensitive currents. Ondansetron in sub-micromolar concentrations inhibits hSK2 currents even under altered ionic conditions.
小电导钙激活钾通道（SK通道）已被提议作为治疗心房颤动的抗心律失常靶点。我们之前证明，5-羟色胺受体拮抗剂昂丹司琼在治疗浓度（即亚微摩尔浓度）下，于生理性细胞外/细胞内[K]梯度中可抑制异源表达的人SK2（hSK2）电流以及天然心脏SK电流。最近一项在对称[K]条件下进行的研究对这一结果提出了质疑。本研究的目的是在对称[K]条件下重新探讨昂丹司琼对hSK2介导电流的抑制作用。采用全细胞膜片钳技术研究昂丹司琼和蜂毒明肽对在HEK 293细胞中表达的hSK2介导电流的影响。在100 nM [Ca]存在的情况下，于对称[K]条件下测量电流。在存在400 nM游离胞质钙的情况下，hSK2的表达产生内向整流的全细胞电流。昂丹司琼抑制全细胞hSK2电流，在-80 mV和40 mV时的IC50值分别为154和113 nM。被昂丹司琼抑制的宏观电流和被蜂毒明肽抑制的电流表现出具有相似反转电位的内向整流电流-电压关系（蜂毒明肽约为5 mV，昂丹司琼约为2 mV）。在持续存在100 nM蜂毒明肽的情况下，1 μM昂丹司琼对hSK2介导的全细胞电流没有影响。野生型HEK 293细胞不表达对昂丹司琼或蜂毒明肽敏感的电流。即使在离子条件改变的情况下，亚微摩尔浓度的昂丹司琼也能抑制hSK2电流。
