Division of Cardiology, Sijhih Cathay General Hospital, Sijhih, Taiwan.
J Card Fail. 2011 Jan;17(1):82-90. doi: 10.1016/j.cardfail.2010.10.002. Epub 2010 Dec 3.
Myocardial fibrosis plays a critical role in heart failure, resulting in cardiac structural and electrical remodeling which can induce atrial arrhythmias. Collagen is the major element of fibrosis. However, it is not clear whether collagen can directly regulate the calcium homeostasis and the electrophysiologic characteristics of cardiomyocytes. The aim of this study was to determine the effects of collagen on calcium homeostasis and the electrical properties of atrial cardiomyocytes.
HL-1 cardiomyocytes were cultured with and without collagen type I (1 or 10 μg/mL) or losartan (10 μmol/L). Whole-cell clamp, indo-1 fluorescence, and Western blotting were used to evaluate the action potential (AP) and ionic currents, intracellular calcium homeostasis, and calcium regulatory proteins. Compared with the control samples, there was no significant difference in collagen (1 μg/mL)-treated HL-1 cardiomyocytes. However, collagen (10 μg/mL)-treated HL-1 cardiomyocytes exhibited larger intracellular calcium (Ca(2+)) transients by 113% and a larger sarcoplasmic reticulum calcium content by 86%. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes had higher expression of sarcoplasmic reticulum ATPase (SERCA2a) and Thr17-phosphorylated phospholamban but similar protein expressions of the Na(+)/Ca(2+) exchanger and ryanodine receptor. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes (n = 11) had larger AP amplitude (104 ± 5 vs 83 ± 7 mV; P < .05), and shorter 90% of AP duration (25 ± 2 vs 33 ± 2 ms, P < .05) than control cells (n = 11). Moreover, collagen (10 μg/mL)-treated HL-1 cells had larger I(to) and I(Ksus) values than control cells. The administration of losartan (10 μmol/L) attenuated collagen-induced changes in Ca(2+) transients, Ca(2+) stores, AP morphology, ionic currents, SERCA2a, and Thr17-phosphorylated phospholamban expressions.
This study demonstrates that collagen can directly modulate the calcium dynamics and electrical activities of atrial cardiomyocytes, which are associated with the renin-angiotensin system. These findings suggest a critical role of collagen in electrical remodeling during fibrosis.
心肌纤维化在心力衰竭中起着关键作用，导致心脏结构和电重构，从而引发心房性心律失常。胶原是纤维化的主要成分。然而，目前尚不清楚胶原是否能直接调节心肌细胞的钙稳态和电生理特性。本研究旨在确定胶原对钙稳态和心房肌细胞电生理特性的影响。
HL-1 心肌细胞在有无胶原 I（1 或 10μg/ml）或氯沙坦（10μmol/L）的情况下培养。采用全细胞膜片钳、indo-1 荧光和 Western blot 技术评价动作电位（AP）和离子电流、细胞内钙稳态和钙调节蛋白。与对照组相比，胶原（1μg/ml）处理的 HL-1 心肌细胞无明显差异。然而，胶原（10μg/ml）处理的 HL-1 心肌细胞的细胞内钙（[Ca（2+）]（i））瞬变增加了 113%，肌浆网钙含量增加了 86%。胶原（10μg/ml）处理的 HL-1 心肌细胞的肌浆网 ATP 酶（SERCA2a）和 Thr17 磷酸化磷蛋白表达增加，但钠钙交换体和兰尼碱受体的蛋白表达相似。胶原（10μg/ml）处理的 HL-1 心肌细胞（n=11）的 AP 幅度（104±5比 83±7mV；P<0.05）和 90%AP 时程（25±2比 33±2ms，P<0.05）均大于对照组（n=11）。此外，胶原（10μg/ml）处理的 HL-1 细胞的 Ito 和 IKsus 值大于对照组细胞。氯沙坦（10μmol/L）可减轻胶原诱导的[Ca（2+）]（i）瞬变、[Ca（2+）]（i）库、AP 形态、离子电流、SERCA2a 和 Thr17 磷酸化磷蛋白表达的变化。
本研究表明，胶原可直接调节心房肌细胞的钙动力学和电活动，这与肾素-血管紧张素系统有关。这些发现提示胶原在纤维化过程中的电重构中起关键作用。
