Unit of Cardiac Physiology, Manchester Academic Health Science Centre, University of Manchester, United Kingdom.
Circ Res. 2024 Sep 13;135(7):739-754. doi: 10.1161/CIRCRESAHA.124.324601. Epub 2024 Aug 14.
Transverse (t)-tubules drive the rapid and synchronous Ca rise in cardiac myocytes. The virtual complete atrial t-tubule loss in heart failure (HF) decreases Ca release. It is unknown if or how atrial t-tubules can be restored and how this affects systolic Ca.
HF was induced in sheep by rapid ventricular pacing and recovered following termination of rapid pacing. Serial block-face scanning electron microscopy and confocal imaging were used to study t-tubule ultrastructure. Function was assessed using patch clamp, Ca, and confocal imaging. Candidate proteins involved in atrial t-tubule recovery were identified by western blot and expressed in rat neonatal ventricular myocytes to determine if they altered t-tubule structure.
Atrial t-tubules were lost in HF but reappeared following recovery from HF. Recovered t-tubules were disordered, adopting distinct morphologies with increased t-tubule length and branching. T-tubule disorder was associated with mitochondrial disorder. Recovered t-tubules were functional, triggering Ca release in the cell interior. Systolic Ca, , sarcoplasmic reticulum Ca content, and sarcoendoplasmic reticulum Ca ATPase function were restored following recovery from HF. Confocal microscopy showed fragmentation of ryanodine receptor staining and movement away from the z-line in HF, which was reversed following recovery from HF. Acute detubulation, to remove recovered t-tubules, confirmed their key role in restoration of the systolic Ca transient, the rate of Ca removal, and the peak L-type Ca current. The abundance of telethonin and myotubularin decreased during HF and increased during recovery. Transfection with these proteins altered the density and structure of tubules in neonatal myocytes. Myotubularin had a greater effect, increasing tubule length and branching, replicating that seen in the recovery atria.
We show that recovery from HF restores atrial t-tubules, and this promotes recovery of , sarcoplasmic reticulum Ca content, and systolic Ca. We demonstrate an important role for myotubularin in t-tubule restoration. Our findings reveal a new and viable therapeutic strategy.
横向（t）-小管驱动心肌细胞中快速和同步的 Ca 上升。心力衰竭（HF）中虚拟完整的心房 t-小管丢失会减少 Ca 释放。目前尚不清楚心房 t-小管是否可以恢复，以及这如何影响收缩期 Ca。
通过快速心室起搏诱导绵羊 HF，并在快速起搏终止后恢复。使用串行块面扫描电子显微镜和共聚焦成像来研究 t-小管超微结构。使用膜片钳、Ca 和共聚焦成像来评估功能。通过 Western blot 鉴定参与心房 t-小管恢复的候选蛋白，并在大鼠乳鼠心室肌细胞中表达，以确定它们是否改变 t-小管结构。
HF 时心房 t-小管丢失，但在 HF 恢复后重新出现。恢复的 t-小管排列紊乱，采用独特的形态，t-小管长度和分支增加。t-小管紊乱与线粒体紊乱有关。恢复的 t-小管是功能性的，可触发细胞内 Ca 释放。HF 恢复后，收缩期 Ca、肌浆网 Ca 含量和肌浆网 Ca ATP 酶功能得到恢复。共聚焦显微镜显示 HF 时肌浆网 Ca 释放通道蛋白染色的片段化和远离 Z 线的运动，HF 恢复后这些改变得到逆转。急性去小管（detubulation），以去除恢复的 t-小管，证实了它们在恢复收缩期 Ca 瞬变、Ca 去除率和峰值 L 型 Ca 电流中的关键作用。在 HF 期间，telethonin 和肌小管蛋白的丰度降低，在恢复期间增加。用这些蛋白转染改变了新生心肌细胞中小管的密度和结构。肌小管蛋白的作用更大，增加了小管的长度和分支，复制了在恢复心房中观察到的变化。
我们表明，HF 恢复会恢复心房 t-小管，这促进了肌浆网 Ca 含量和收缩期 Ca 的恢复。我们证明了肌小管蛋白在 t-小管恢复中的重要作用。我们的发现揭示了一种新的可行的治疗策略。
