Moench I, Lopatin A N
Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
J Mol Cell Cardiol. 2014 Jul;72:374-83. doi: 10.1016/j.yjmcc.2014.04.011. Epub 2014 Apr 28.
We have recently shown that in mouse ventricular myocytes, t-tubules can be quickly and tightly sealed during the resolution of hyposmotic shock of physiologically relevant magnitude. Sealing of t-tubules is associated with trapping extracellular solution inside the myocytes but the ionic homeostasis of sealed t-tubules and the consequences of potential transtubular ion fluxes remain unknown. In this study we investigated the dynamics of Ca(2+) movements associated with sealing of t-tubules. The data show that under normal conditions sealed t-tubules contain Ca(2+) at concentrations below 100μM. However, blockade of voltage-dependent Ca(2+) channels with 10μM nicardipine, or increasing extracellular concentration of K(+) from 5.4mM to 20mM led to several fold increase in concentration of t-tubular Ca(2+). Alternatively, the release of Ca(2+) from sarcoplasmic reticulum using 10mM caffeine led to the restoration of t-tubular Ca(2+) towards extracellular levels within few seconds. Sealing of t-tubules in the presence of extracellular 1.5mM Ca(2+) and 5.4mM extracellular K(+) led to occasional and sporadic intracellular Ca(2+) transients. In contrast, sealing of t-tubules in the presence of 10mM caffeine was characterized by a significant long lasting increase in intracellular Ca(2+). The effect was completely abolished in the absence of extracellular Ca(2+) and significantly reduced in pre-detubulated myocytes but was essentially preserved in the presence of mitochondrial decoupler dinitrophenol. This study shows that sealed t-tubules are capable of highly regulated transport of Ca(2+) and present a major route for Ca(2+) influx into the cytosol during sealing process.
我们最近发现，在小鼠心室肌细胞中，当生理相关强度的低渗休克消退时，横管（t-小管）可迅速且紧密地封闭。横管的封闭与细胞内捕获细胞外溶液有关，但封闭的横管的离子稳态以及潜在的跨管离子通量的后果仍不清楚。在本研究中，我们研究了与横管封闭相关的Ca(2+)运动动力学。数据表明，在正常条件下，封闭的横管中Ca(2+)浓度低于100μM。然而，用10μM尼卡地平阻断电压依赖性Ca(2+)通道，或将细胞外K(+)浓度从5.4mM增加到20mM，会导致横管Ca(2+)浓度增加几倍。或者，使用10mM咖啡因从肌浆网释放Ca(2+)，会在几秒钟内使横管Ca(2+)恢复到细胞外水平。在细胞外1.5mM Ca(2+)和5.4mM细胞外K(+)存在的情况下封闭横管，会导致偶尔和零星的细胞内Ca(2+)瞬变。相比之下，在10mM咖啡因存在的情况下封闭横管的特征是细胞内Ca(2+)显著持久增加。在没有细胞外Ca(2+)的情况下，这种效应完全消失，在预先去管的肌细胞中显著降低，但在存在线粒体解偶联剂二硝基苯酚的情况下基本保持不变。这项研究表明，封闭的横管能够高度调节Ca(2+)的转运，并在封闭过程中成为Ca(2+)流入细胞质的主要途径。
