目的:心房颤动(AF)与转录因子Pitx2c的表达改变以及钙释放诱导的后去极化的高发生率有关。然而,Pitx2c表达与钙稳态缺陷之间的关系尚不清楚,我们在此旨在确定Pitx2c表达如何影响肌浆网(SR)的钙释放及其对离体心房肌细胞电活动的影响.
方法:要解决此问题,我们将共聚焦钙成像和膜片钳技术应用于从有条件心房特异性Pitx2c缺失的小鼠模型中分离的心房肌细胞.
结果:我们的研究结果表明,Pitx2c的杂合缺失使钙火花频率加倍,将火花/站点的频率增加1.5倍,钙火花衰减常数从36到42ms,波频率从无到3.2min-1。此外,细胞电容增加了30%,SR钙负载和瞬态内向电流(ITI)频率均增加了一倍。此外,具有自发动作电位的细胞比例从无增加到44%。Pitx2c缺乏对左右心房肌细胞的影响相当,Pitx2c的纯合缺失对火花没有任何进一步的影响,SR钙负荷,ITI频率或自发动作电位。
结论:我们的研究结果表明,杂合子Pitx2c缺失诱导钙稳态和电活动的缺陷,这模拟了房颤患者右心房肌细胞中观察到的紊乱,并表明Pitx2c缺陷赋予了房颤的细胞电生理标志给分离的心房肌细胞。
OBJECTIVE: Atrial fibrillation (AF) has been associated with altered expression of the transcription factor Pitx2c and a high incidence of calcium release-induced
afterdepolarizations. However, the relationship between Pitx2c expression and defective calcium homeostasis remains unclear and we here aimed to determine how Pitx2c expression affects calcium release from the sarcoplasmic reticulum (SR) and its impact on electrical activity in isolated atrial myocytes.
METHODS: To address this issue, we applied confocal calcium imaging and patch-clamp techniques to atrial myocytes isolated from a mouse model with conditional atrial-specific deletion of Pitx2c.
RESULTS: Our findings demonstrate that heterozygous deletion of Pitx2c doubles the calcium spark frequency, increases the frequency of sparks/site 1.5-fold, the calcium spark decay constant from 36 to 42 ms and the wave frequency from none to 3.2 min-1. Additionally, the cell capacitance increased by 30% and both the SR calcium load and the transient inward current (ITI) frequency were doubled. Furthermore, the fraction of cells with spontaneous action potentials increased from none to 44%. These effects of Pitx2c deficiency were comparable in right and left atrial myocytes, and homozygous deletion of Pitx2c did not induce any further effects on sparks, SR calcium load, ITI frequency or spontaneous action potentials.
CONCLUSIONS: Our findings demonstrate that heterozygous Pitx2c deletion induces defects in calcium homeostasis and electrical activity that mimic derangements observed in right atrial myocytes from patients with AF and suggest that Pitx2c deficiency confers cellular electrophysiological hallmarks of AF to isolated atrial myocytes.