Calcium binding kinetics of troponin C strongly modulate cooperative activation and tension kinetics in cardiac muscle
Calcium binding kinetics of troponin C strongly modulate cooperative activation and tension kinetics in cardiac muscle
复制标题
DOI：
10.1016/j.yjmcc.2010.10.025
复制
发表时间：
2011-01-01
影响因子：
5
通讯作者：
Regnier, Michael
中科院分区：
文献类型：
--
作者：
Kreutziger, Kareen L.;Piroddi, Nicoletta;Regnier, Michael
心肌的张力发展和松弛是通过Ca2+与心肌肌钙蛋白C （cTnC）的结合和强交叉桥结合在细丝上调节的。然而，cTnC Ca2+结合特性对心肌肌瘤组织结构中这些过程的影响尚不清楚，可能与骨骼肌不同。为了研究这一点，我们产生了cTnC的单氨基酸变体，改变了Ca2+解离率（k(off)），通过停止流动光谱在全肌钙蛋白（cTn）复合物中测量（I61Q cTn>WT cTn>L48Q cTn），并将它们交换成心肌原纤维和脱膜小梁。在Ca2+饱和状态下的肌原纤维中，L48Q cTnC不影响最大张力（T-max）、细丝激活（k(ACT)）和张力发展（k(TR)）速率或弛豫速率，但增加了慢相弛豫的持续时间。相比之下，I61Q cTnC使T-max、k（ACT）、k（TR）和k（TR）降低40-65%，而弛豫变化不大。有趣的是，I61Q cTnC的k（ACT）小于k(TR)，并且随着无机磷酸盐的加入，这种差异增加，这表明降低的cTnC Ca2+亲和力可以限制细丝的活化动力学。与I61Q cTn交换的小梁降低了张力-pCa的T-max、Ca2+敏感性（pCa(50)）和斜率（n(H)），而L48Q cTn增加了pCa(50)，降低了n(H)。增加2-脱氧atp的过桥循环增加WT或L48Q cTn的pCa(50)，但不增加I61Q cTn。我们讨论了这些结果对理解cTn Ca2+结合特性在心肌张力发展和松弛的幅度和速率上的作用的影响。(C) 2010 Elsevier Ltd.版权所有。
Tension development and relaxation in cardiac muscle are regulated at the thin filament via Ca2+ binding to cardiac troponin C (cTnC) and strong cross-bridge binding. However, the influence of cTnC Ca2+-binding properties on these processes in the organized structure of cardiac sarcomeres is not well-understood and likely differs from skeletal muscle. To study this we generated single amino acid variants of cTnC with altered Ca2+ dissociation rates (k(off)), as measured in whole troponin (cTn) complex by stopped-flow spectroscopy (I61Q cTn>WT cTn>L48Q cTn), and exchanged them into cardiac myofibrils and demembranated trabeculae. In myofibrils at saturating Ca2+, L48Q cTnC did not affect maximum tension (T-max), thin filament activation (k(ACT)) and tension development (k(TR)) rates, or the rates of relaxation, but increased duration of slow phase relaxation. In contrast, I61Q cTnC reduced T-max, k(ACT) k(TR) and k(TR) by 40-65% with little change in relaxation. Interestingly, k(ACT) was less than k(TR) with I61Q cTnC, and this difference increased with addition of inorganic phosphate, suggesting that reduced cTnC Ca2+-affinity can limit thin filament activation kinetics. Trabeculae exchanged with I61Q cTn had reduced T-max, Ca2+ sensitivity of tension (pCa(50)), and slope (n(H)) of tension-pCa, while L48Q cTn increased pCa(50) and reduced n(H). Increased cross-bridge cycling with 2-deoxy-ATP increased pCa(50) with WT or L48Q cTn, but not I61Q cTn. We discuss the implications of these results for understanding the role of cTn Ca2+-binding properties on the magnitude and rate of tension development and relaxation in cardiac muscle. (C) 2010 Elsevier Ltd. All rights reserved.