Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey.
J Physiol Biochem. 2011 Sep;67(3):317-30. doi: 10.1007/s13105-011-0077-3. Epub 2011 Feb 2.
Hearts from subjects with different ages have different Ca(2+) signaling. Release of Ca(2+) from intracellular stores in response to an action potential initiates cardiac contraction. Both depolarization-stimulated and spontaneous Ca(2+) releases, Ca(2+) transients and Ca(2+) sparks, demonstrate the main events of excitation-contraction coupling (ECC). Global increase in free Ca(2+) concentration (Ca(2+)) consists of summation of Ca(2+) release events in cardiomyocytes. Since the Ca(2+) flux induced by Ca(2+) sparks reports a summation of ryanodine-sensitive Ca(2+) release channels (RyR2s)'s behavior in a spark cluster, evaluation of the properties of Ca(2+) sparks and Ca(2+) transients may provide insight into the role of RyR2s on altered heart function between 3-month-old (young adult) and 6-month-old (mature adult) rats. Basal Ca(2+) and Ca(2+) sparks frequency were significantly higher in mature adult rats compared to those of young adults. Moreover, amplitudes of Ca(2+) sparks and Ca(2+) transients were significantly smaller in mature adults than those of young adults with longer time courses. A smaller L-type Ca(2+) current density and decreased SR Ca(2+) load was observed in mature adult rats. In addition, RyR2s were markedly hyperphosphorylated, and phosphorylation levels of PKA and CaMKII were higher in heart from mature adults compared to those of young adults, whereas their SERCA protein levels were similar. Our data demonstrate that hearts from rats with different ages have different Ca(2+) signaling including hyperphosphorylation of RyR2s and higher basal Ca(2+) together with increased oxidized protein-thiols in mature adult rats compared to those of young adults, which play important roles in ECC. Finally, we report that ECC efficiency changes with age during maturation, partially related with an increased cellular oxidation level leading to reduced free protein-thiols in cardiomyocytes.
不同年龄供体心脏的钙离子信号不同。动作电位引发细胞内钙库释放钙离子，启动心脏收缩。去极化刺激和自发性钙离子释放、钙离子瞬变和钙离子火花，均显示出兴奋-收缩偶联（ECC）的主要事件。细胞内游离钙离子浓度（[Ca2+]i）的整体增加，由心肌细胞钙离子释放事件的总和组成。由于钙离子火花所诱导的钙离子流，反映了钙离子火花簇中 Ryanodine 敏感钙离子释放通道（RyR2s）的行为总和，因此评估钙离子火花和钙离子瞬变的特性，可以深入了解 RyR2s 在 3 个月大（青年成年）和 6 个月大（成熟成年）大鼠之间改变心脏功能中的作用。与青年成年大鼠相比，成熟成年大鼠的基础 [Ca2+]i 和钙离子火花频率明显更高。此外，成熟成年大鼠的钙离子火花和钙离子瞬变幅度明显小于青年成年大鼠，且具有更长的时程。成熟成年大鼠的 L 型钙离子电流密度较小，SR 钙离子负荷降低。此外，RyR2s 明显过度磷酸化，成熟成年大鼠心脏的 PKA 和 CaMKII 磷酸化水平高于青年成年大鼠，而其 SERCA 蛋白水平相似。我们的数据表明，不同年龄供体心脏的钙离子信号不同，包括 RyR2s 的过度磷酸化、基础 [Ca2+]i 升高，以及成熟成年大鼠比青年成年大鼠具有更高的氧化蛋白巯基，这些在 ECC 中起着重要作用。最后，我们报告 ECC 效率在成熟过程中随年龄变化，部分与细胞氧化水平增加有关，导致心肌细胞中游离蛋白巯基减少。
