Progress in Biophysics and Molecular Biology ( IF 3.8 ) Pub Date : 2019-11-16 , DOI: 10.1016/j.pbiomolbio.2019.11.004 C M Zgierski-Johnston 1 , S Ayub 2 , M C Fernández 1 , E A Rog-Zielinska 1 , F Barz 2 , O Paul 3 , P Kohl 1 , P Ruther 3
Optogenetics enables cell-type specific monitoring and actuation via light-activated proteins. In cardiac research, expressing light-activated depolarising ion channels in cardiomyocytes allows optical pacing and defibrillation. Previous studies largely relied on epicardial illumination. Light penetration through the myocardium is however problematic when moving to larger animals and humans. To overcome this limitation, we assessed the utility of an implantable multi light-emitting diode (LED) optical probe (IMLOP) for intramural pacing of mouse hearts expressing cardiac-specific channelrhodopsin-2 (ChR2).
Here we demonstrated that IMLOP insertion needs approximately 20 mN of force, limiting possible damage from excessive loads applied during implantation. Histological sections confirmed the confined nature of tissue damage during acute use. The temperature change of the surrounding tissue was below 1 K during LED operation, rendering the probe safe for use in situ. This was confirmed in control experiments where no effect on cardiac action potential conduction was observed even when using stimulation parameters twenty-fold greater than required for pacing.
In situ experiments on ChR2-expressing mouse hearts demonstrated that optical stimulation is possible with light intensities as low as 700 μW/mm2; although stable pacing requires higher intensities. When pacing with a single LED, rheobase and chronaxie values were 13.3 mW/mm2 ± 0.9 mW/mm2 and 3 ms ± 0.6 ms, respectively. When doubling the stimulated volume the rheobase decreased significantly (6.5 mW/mm2 ± 0.9 mW/mm2).
We have demonstrated IMLOP-based intramural optical pacing of the heart. Probes cause locally constrained tissue damage in the acute setting and require low light intensities for pacing. Further development is necessary to assess effects of chronic implantation.
中文翻译:
在表达视紫红质的小鼠心脏中使用透壁多LED探针进行心脏起搏。
光遗传学使得能够通过光激活蛋白对细胞类型进行特定的监测和激活。在心脏研究中,在心肌细胞中表达光激活的去极化离子通道可以进行光学起搏和除颤。先前的研究主要依靠心外膜照射。然而,当移至较大的动物和人类时,穿过心肌的光穿透是有问题的。为了克服此限制,我们评估了植入式多发光二极管(LED)光学探针(IMLOP)在表达心脏特异性Channelrhodopsin-2(ChR2)的小鼠心脏的壁内起搏中的实用性。
在这里,我们证明了IMLOP插入需要大约20 mN的力,从而限制了植入期间施加的超负荷可能造成的损坏。组织学切片证实了急性使用期间组织损伤的局限性。在LED操作过程中,周围组织的温度变化低于1 K,从而使探头可安全就地使用。在对照实验中证实了这一点,即使使用比起搏所需的刺激参数大二十倍的刺激参数,也未观察到对心脏动作电位传导的影响。
在表达ChR2的小鼠心脏上进行的原位实验表明,光强度低至700μW/ mm 2时可能产生光刺激; 尽管稳定的起搏需要更高的强度。当使用单个LED起搏时,流变基和时轴值分别为13.3 mW / mm2±0.9 mW / mm 2和3 ms±0.6 ms。当使受激体积增加一倍时,流变碱显着降低(6.5 mW / mm2±0.9 mW / mm 2)。
我们已经证明了基于IMLOP的心脏壁内光学起搏。探针在急性环境中会造成局部受限的组织损伤,并且需要低光强度才能起搏。有必要进一步发展以评估慢性植入的效果。