Department of Physiology, Fukuoka University School of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
Department of Cardiology, Zhongda Hospital, Southeast University, Nanjing, Jiangsu 210009, China.
Cardiovasc Res. 2017 Aug 1;113(10):1243-1255. doi: 10.1093/cvr/cvx117.
Transient receptor potential cation channel subfamily melastatin member 4 (TRPM4), a Ca2+-activated nonselective cation channel abundantly expressed in the heart, has been implicated in conduction block and other arrhythmic propensities associated with cardiac remodelling and injury. The present study aimed to quantitatively evaluate the arrhythmogenic potential of TRPM4.
Patch clamp and biochemical analyses were performed using expression system and an immortalized atrial cardiomyocyte cell line (HL-1), and numerical model simulation was employed. After rapid desensitization, robust reactivation of TRPM4 channels required high micromolar concentrations of Ca2+. However, upon evaluation with a newly devised, ionomycin-permeabilized cell-attached (Iono-C/A) recording technique, submicromolar concentrations of Ca2+ (apparent Kd = ∼500 nM) were enough to activate this channel. Similar submicromolar Ca2+ dependency was also observed with sharp electrode whole-cell recording and in experiments coexpressing TRPM4 and L-type voltage-dependent Ca2+ channels. Numerical simulations using a number of action potential (AP) models (HL-1, Nygren, Luo-Rudy) incorporating the Ca2+- and voltage-dependent gating parameters of TRPM4, as assessed by Iono-C/A recording, indicated that a few-fold increase in TRPM4 activity is sufficient to delay late AP repolarization and further increases (≥ six-fold) evoke early afterdepolarization. These model predictions are consistent with electrophysiological data from angiotensin II-treated HL-1 cells in which TRPM4 expression and activity were enhanced.
These results collectively indicate that the TRPM4 channel is activated by a physiological range of Ca2+ concentrations and its excessive activity can cause arrhythmic changes. Moreover, these results demonstrate potential utility of the first AP models incorporating TRPM4 gating for in silico assessment of arrhythmogenicity in remodelling cardiac tissue.
瞬时受体电位阳离子通道亚家族 melastatin 成员 4（TRPM4）是一种在心脏中丰富表达的 Ca2+激活的非选择性阳离子通道，与心脏重构和损伤相关的传导阻滞和其他心律失常倾向有关。本研究旨在定量评估 TRPM4 的致心律失常潜力。
使用表达系统和永生化心房肌细胞系（HL-1）进行膜片钳和生化分析，并进行数值模型模拟。在快速脱敏后，需要高微摩尔浓度的 Ca2+才能使 TRPM4 通道重新激活。然而，在用新设计的离子霉素通透细胞贴附（Iono-C/A）记录技术进行评估时，亚微摩尔浓度的 Ca2+（表观 Kd=∼500 nM）足以激活该通道。在Sharp 电极全细胞记录和共表达 TRPM4 和 L 型电压依赖性 Ca2+通道的实验中也观察到类似的亚微摩尔 Ca2+依赖性。使用几种动作电位（AP）模型（HL-1、Nygren、Luo-Rudy）进行数值模拟，这些模型整合了通过 Iono-C/A 记录评估的 TRPM4 的 Ca2+和电压依赖性门控参数，表明 TRPM4 活性增加几倍足以延迟晚期 AP 复极，进一步增加（≥六倍）会引发早期后除极。这些模型预测与血管紧张素 II 处理的 HL-1 细胞中的电生理数据一致，其中 TRPM4 的表达和活性增强。
这些结果共同表明，TRPM4 通道被生理范围内的 Ca2+浓度激活，其过度活动可引起心律失常变化。此外，这些结果表明，包含 TRPM4 门控的第一个 AP 模型可用于计算机模拟评估重构心脏组织中的致心律失常性。
