Actin removal from cardiac myocytes shows that near Z line titin attaches to actin while under tension.
Actin removal from cardiac myocytes shows that near Z line titin attaches to actin while under tension.
复制标题
从心肌细胞中去除肌动蛋白表明，在张力下，Z 线附近的肌动蛋白会附着在肌动蛋白上。
DOI：
10.1152/ajpcell.1997.273.2.c662
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Granzier,H
中科院分区：
文献类型：
--
作者：
Trombitas,K;Granzier,H
心脏肌节的 I 带包含肌动蛋白和肌联蛋白/连接蛋白丝。早期的研究表明肌联蛋白与肌动蛋白原位结合。这种相互作用在肌动蛋白表现弹性的 I 带区域一定很弱。另一方面，在邻近 Z 线的大约 100 nm 宽的区域中，肌联蛋白可能与肌动蛋白强烈结合，在该区域中肌联蛋白被发现是无弹性的。为了研究肌动蛋白和肌动蛋白之间假定的相互作用，需要从 I 带不同区域选择性去除肌动蛋白的技术。在此，我们报告了凝溶胶蛋白片段 (FX-45) 和从大鼠心肌细胞中提取肌动蛋白的研究。肌动蛋白提取是双相的：大部分肌动蛋白在大约 10 分钟内提取，而 Z 线附近的肌动蛋白（肌动蛋白无弹性）需要大约 10 倍的提取时间。因此，通过控制提取时间，我们可以去除 Z 线之外的完整肌动蛋白丝，或者仅去除延伸到毗邻 Z 线的肌动蛋白非弹性区域之外的肌动蛋白丝片段。无肌动蛋白丝的 I 带包含肌动蛋白丝，通常具有从每个粗丝延伸出的一根丝。此外，我们还观察到一条深色横线（连接线），其在肌节中的位置随肌节长度线性变化。连接线的肌节位置与抗肌联蛋白抗体9D10的结合位点一致。肌动蛋白的去除显着影响松弛肌节的长度。对照细胞中的松弛肌节长度为 1.85 +/- 0.04 微米，并在 Z 线附近的肌动蛋白被提取后减少到 1.71 +/- 0.05 微米。这种长度的减少可能是由于 Z 线附近的肌动蛋白去除后暴露的肌动蛋白片段的收缩引起的，这表明肌动蛋白不仅附着在肌动蛋白丝上，而且还处于张力下。
The I band of cardiac sarcomeres contains both actin and titin/connectin filaments. Earlier work has suggested that titin binds to actin in situ. This interaction must be weak in the region of the I band where titin behaves elastically. On the other hand, titin may bind strongly to actin in the approximately 100-nm-wide region adjoining the Z line, where titin has been found to be inelastic. To study the putative interaction between titin and actin, techniques for selective removal of actin from different regions of the I band are needed. Here we report studies with a gelsolin fragment (FX-45) and extract actin from rat cardiac myocytes. Actin extraction was biphasic: the majority of actin was extracted in approximately 10 min, whereas actin near the Z line (where titin is inelastic) required a approximately 10-fold longer extraction time. Thus, by controlling the extraction time, we could remove either the full actin filament outside the Z line or just the segment of the actin filament that extends beyond the inelastic region of titin that adjoins the Z line. The actin filament-free I band contained titin filaments, typically with one filament extending from each thick filament. In addition, we observed a dark transverse line (junction line), the location of which in the sarcomere varied linearly with sarcomere length. The position in the sarcomere of the junction line coincided with the binding site of the anti-titin antibody 9D10. Actin removal significantly affected the slack sarcomere length. Slack sarcomere length was 1.85 +/- 0.04 microns in control cells and decreased to 1.71 +/- 0.05 microns after actin near the Z line was extracted. This length reduction may be caused by contraction of the titin segment that becomes exposed after actin removal near the Z line, indicating that titin is not only attached to the actin filament but is also under tension.