Solute movement in the t-tubule system of rabbit and mouse cardiomyocytes.
Solute movement in the t-tubule system of rabbit and mouse cardiomyocytes.
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DOI：
10.1073/pnas.1805979115
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发表时间：
2018-07-24
影响因子：
11.1
通讯作者：
Cannell MB
中科院分区：
文献类型：
--
作者：
Kong CHT;Rog-Zielinska EA;Kohl P;Orchard CH;Cannell MB
表面膜的微小内陷，称为T管，将电信号和化学信号传入心肌细胞。先前的研究发现T管内溶质交换速率缓慢，并表明扩散可能受到高度限制。通过结合荧光示踪剂测量和详细的计算模型，我们表明小分子溶质（1 kDa）在T管内似乎几乎可以自由移动，与自由扩散相比，交换速率减慢约5 - 16倍，大部分是由T管的几何形状效应引起的。较大的溶质（>4 kDa）进入T管受限，并且T管开口结构的差异也可能阻碍物种依赖性的进入。我们的数据和分析为理解疾病诱导的T管紊乱如何导致细胞功能改变提供了一条新途径。
心脏横（T -）管将电兴奋和溶质向细胞中心运输，但它们运输小分子的能力尚不清楚。虽然光漂白后的荧光恢复（FRAP）可以提供一种测量局部溶质运动的方法，但扩散系数的提取因细胞和照明光束的几何形状而变得复杂。在这项研究中，我们利用测量的细胞几何形状和详细的计算机模型来推导兔和小鼠心室心肌细胞T管系统内1 - kDa溶质的表观扩散系数。这种方法表明单个T管内的扩散比先前报道的要快。T管的曲折度、膨大和纵向成分的存在共同显著降低了溶质运动的表观速率。在稳态下，大（>4 kDa）溶质不能自由填充两种物种的T管腔，并且对于>70 kDa的溶质，只有不到50%的T管体积可用。对FRAP数据的详细模型拟合表明，溶质扩散在T管入口处还受到额外限制，这种效应在小鼠中比在兔中更明显。利用电子显微镜和断层扫描技术研究了这种效应可能的结构基础。在细胞表面附近，小鼠T管更曲折，并充满一种电子致密的基质，先前已确定为糖萼和一种多阴离子网。兔和小鼠T管网络中的溶质运动似乎可以由它们不同的几何特性来解释，这影响了使用这些物种来理解T管功能以及与T管疾病相关变化的后果。
Microscopic invaginations of the surface membrane, called t-tubules, carry electrical and chemical signals into cardiomyocytes. Previous studies have found slow rates of solute exchange inside t-tubules and have suggested that diffusion may be highly restricted. By combining fluorescent tracer measurements and detailed computational modeling, we show that small solutes (1 kDa) appear to move almost freely within t-tubules and most of the ∼5–16× slowing in exchange rate, compared with free diffusion, arises from t-tubule geometry effects. Larger solutes (>4 kDa) show restricted access into t-tubules, and species-dependent entry may also be impeded by differences in t-tubule mouth configuration. Our data and analyses provide a new pathway to understanding how disease-induced t-tubule derangement may contribute to altered cellular function. Cardiac transverse (t-) tubules carry both electrical excitation and solutes toward the cell center but their ability to transport small molecules is unclear. While fluorescence recovery after photobleaching (FRAP) can provide an approach to measure local solute movement, extraction of diffusion coefficients is confounded by cell and illumination beam geometries. In this study, we use measured cellular geometry and detailed computer modeling to derive the apparent diffusion coefficient of a 1-kDa solute inside the t-tubular system of rabbit and mouse ventricular cardiomyocytes. This approach shows that diffusion within individual t-tubules is more rapid than previously reported. T-tubule tortuosity, varicosities, and the presence of longitudinal elements combine to substantially reduce the apparent rate of solute movement. In steady state, large (>4 kDa) solutes did not freely fill the t-tubule lumen of both species and <50% of the t-tubule volume was available to solutes >70 kDa. Detailed model fitting of FRAP data suggests that solute diffusion is additionally restricted at the t-tubular entrance and this effect was larger in mouse than in rabbit. The possible structural basis of this effect was investigated using electron microscopy and tomography. Near the cell surface, mouse t-tubules are more tortuous and filled with an electron-dense ground substance, previously identified as glycocalyx and a polyanionic mesh. Solute movement in the t-tubule network of rabbit and mouse appears to be explained by their different geometric properties, which impacts the use of these species for understanding t-tubule function and the consequences of changes associated with t-tubule disease.
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影响因子：
3.7
作者：
Crossman DJ;Ruygrok PN;Soeller C;Cannell MB
通讯作者：
Cannell MB
影响因子：
82.9
作者：
通讯作者：
--
影响因子：
4.2
作者：
NITSCHE, JM;BALGI, G
通讯作者：
BALGI, G
影响因子：
3
作者：
Kremer, JR;Mastronarde, DN;McIntosh, JR
通讯作者：
McIntosh, JR
影响因子：
5.5
作者：
Edwards, Joshua N.;Launikonis, Bradley S.
通讯作者：
Launikonis, Bradley S.