The experiment is beautiful, but…

Kirill Stasevich, "Science and Life" 

Although pacemakers save many lives – according to statistics, more than 3 million people around the world carry such devices – their use is associated with certain inconveniences. An electrocardiostimulator, or an artificial pacemaker, helps to restore the normal frequency and frequency of heart contractions – otherwise, rhythm disorders can lead to quite severe consequences for the whole body, up to death. But in order for the rhythm driver to work, its electrodes need to be implanted in the heart, the wires from them connected to a pulse generator, which is implanted under the skin. 

Over time, pacemakers became smaller and smaller, and electrodes with wires became possible to be inserted into the heart using a catheter simply through the veins. However, no matter how small the stimulator is and no matter how thin its wires are, it still needs to change the batteries, and this means an inevitable operation, albeit a small one. In addition, wiring with electrodes stretching to the heart can wear out, and from time to time they also need to be changed. On the other hand, due to the need to pull wires, we cannot put the stimulator wherever we want, and we cannot use many points for stimulation. The heart itself does not always "like" being stimulated by an external device. Finally, if we are talking about children, then it is not always possible to put an artificial rhythm driver for them at all. 

Udi Nussinovitch and Lior Gepstein from the Israeli Technion Institute of Technology have proposed a kind of model of a pacemaker that has no wires, no electrodes, no batteries and that works literally in the light (The Illuminated Heart). In fact, there is no stimulator in the form of an external device at all – the researchers introduced an optogenetic modification into the heart cells, which made it possible to control heart contractions. The general meaning of optogenetic methods is that a light–sensitive protein gene is introduced into the cell - such a protein, embedded in the cell membrane, opens ion channels in the membrane in response to a light pulse. And as we know, it is the redistribution of ions on both sides of the membrane that creates the electrochemical pulse. Optogenetics has found the widest use in neuroscience: by introducing a light-sensitive protein into a neuron, we can arbitrarily, with the help of light signals, generate a signal in a chain of neurons. 

But the heart rate also depends on electrochemical impulses (recall that, although there are fibers of the autonomic nervous system in the heart, some special myocardial cells can generate rhythmic signals themselves, forming the so-called conducting system of the heart). And nothing prevents the introduction of an optogenetic mechanism into the heart. 

The researchers did just that: with the help of a special "domesticated" virus, they introduced an algal photosensitive protein ChR2 (channelrhodopsin-2), reacting to blue light, into the ventricles of the rat heart. (Unicellular green algae, like chlamydomonas, this protein helps to look for more illuminated places.) In an article in Nature Biotechnology (Optogenetics for in vivo cardiac pacing and resynchronization therapies), the authors write that they could adjust the heart rate of animals using blue flashes. The virus allows you to deliver protein to a variety of areas of the heart muscle, so you can control the heart with greater efficiency, because many cells from different places respond to an external signal here at once. 

To "turn on" the optoprotein, no electrodes are needed: blue light from the outside, although it penetrates through living tissues rather poorly, can still reach the heart. But – only if we are talking about a rat. A little bit of a large animal, not to mention a person, has a deeper heart, so here you need to think about how long a light wave can reach it and, accordingly, what kind of light-sensitive protein is needed. The red and infrared regions of the spectrum could be suitable here, and if it comes to experiments with primates, these are the waves that will be used. 

It is worth noting, however, that there are other approaches to creating a wireless pacemaker. About a year ago, we wrote about the development of Stanford University employees who proposed to support the work of a pacemaker using an electromagnetic wave generator located simply on the surface of the body. Another idea belongs to researchers from the University of Illinois at Urbana-Champaign – they were able to make the pacemaker work from the heart muscle itself, due to the energy of its contractions. But, of course, the optogenetic approach looks the most radical – there is no need to implant any device in the heart at all.