Dilated cardiomyopathy (DCM) is a major risk factor for heart failure and is associated with the development of life-threatening cardiac arrhythmias. Using a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model harbouring a mutation in cardiac troponin T (R173W), we aim to examine the cellular basis of arrhythmogenesis in DCM patients with this mutation. iPSC from control (Ctrl) and DCM-TnT-R173W donors from the same family were differentiated into iPSC-CM and analysed through optical action potential (AP) recordings, simultaneous measurement of cytosolic calcium concentration ([Ca²⁺]_i) and membrane currents and separately assayed using field stimulation to detect the threshold for AP- and [Ca²⁺]_i-alternans development. AP duration was unaltered in TnT-R173W iPSC-CM. Nevertheless, TnT-R173W iPSC-CM showed a strikingly low stimulation threshold for AP- and [Ca²⁺]_i-alternans. Myofilaments are known to play a role as intracellular Ca²⁺ buffers and here we show increased Ca²⁺ affinity of intracellular buffers in TnT-R173W cells, indicating increased myofilament sensitivity to Ca²⁺. Similarly, EMD57033, a myofilament Ca²⁺ sensitiser, replicated the abnormal [Ca²⁺]_i dynamics observed in TnT-R173W samples and lowered the threshold for alternans development. In contrast, application of a Ca²⁺ desensitiser (blebbistatin) to TnT-R173W iPSC-CM was able to phenotypically rescue Ca²⁺ dynamics, normalising Ca²⁺ transient profile and minimising the occurrence of Ca²⁺ alternans at physiological frequencies. This finding suggests that increased Ca²⁺ buffering likely plays a major arrhythmogenic role in patients with DCM, specifically in those with mutations in cardiac troponin T. In addition, we propose that modulation of myofilament Ca²⁺ sensitivity could be an effective anti-arrhythmic target for pharmacological management of this disease.

扩张型心肌病 (DCM) 是心力衰竭的主要危险因素，并且与危及生命的心律失常的发展有关。我们使用含有心肌肌钙蛋白 T (R173W) 突变的患者特异性诱导多能干细胞衍生心肌细胞 (iPSC-CM) 模型，旨在检查具有这种突变的 DCM 患者心律失常发生的细胞基础。来自同一家族的对照 (Ctrl) 和 DCM-TnT-R173W 供体的 iPSC 分化为 iPSC-CM，并通过光学动作电位 (AP) 记录、同时测量细胞溶质钙浓度 ([Ca ²⁺ ] _i ) 和细胞膜进行分析电流并使用场刺激分别测定以检测 AP- 和 [Ca ²⁺ ] _i的阈值-交替发展。AP 持续时间在 TnT-R173W iPSC-CM 中没有改变。尽管如此，TnT-R173W iPSC-CM 对 AP- 和 [Ca ²⁺ ] _i -交替显示出惊人的低刺激阈值。^{已知肌丝作为细胞内 Ca 2+}缓冲液发挥作用，在这里我们显示TnT-R173W 细胞中细胞内缓冲液的Ca ^{2+亲和力增加，表明肌丝对 Ca 2+}的敏感性增加。类似地，肌丝 Ca ²⁺敏化剂 EMD57033 复制了在 TnT-R173W 样本中观察到的异常 [Ca ²⁺ ] _{i动力学，并降低了交替发展的阈值。}相反，应用 Ca ²⁺对 TnT-R173W iPSC-CM 的脱敏剂（blebbistatin）能够在表型上挽救 Ca ^{2+动力学，使 Ca 2+}瞬态分布正常化并最大限度地减少生理频率下 Ca ^{2+交替的出现。}这一发现表明，增加的 Ca ²⁺缓冲可能在 DCM 患者中起主要的致心律失常作用，特别是在心肌肌钙蛋白 T 突变的患者中。此外，我们提出调节肌丝 Ca ²⁺敏感性可能是一种有效的抗心律失常药物这种疾病的药物管理目标。