The first optical pacemaker
According to a short news release from the Optical Society of America (OSA), an international team of scientists at Osaka University in Japan has used a femtosecond laser pacemaker to control heart muscle cells. So far, this optical pacemaker will only be used for laboratory research. As writes OSA, 'exposing heart muscle cells to powerful laser pulses can have its drawbacks. Although the laser pulses last for less than a trillionth of a second, damaging effects can build up over time and this currently limits the possibility of clinical applications.' Still, it's a very interesting new technique to study the heart. But read more...
Here is how this optical pacemaker works. You can see above several pictures showing a "laser actuation of a single cultured cardiomyocyte by irradiation, causing it to contract and stay contracted. The image sequence was taken by phase contrast microscopy and the outline of the cell is highlighted. The laser was focused inside the cell using 30 mW of average power, and 8 ms exposures occurred at 1 Hz intervals. The time sequence is (a) 1 sec, (b) 8 sec, (c) 14.7 sec, and (d) 16.7 sec." (Credit: Osaka University)
[Note: Here is a definition of what are "cardiomyocytes" provided by Osaka University. They "are the muscle cells that provide for the contractility of bulk heart tissue. They exhibit a fascinating and complex range of dynamic behavior that forms the building blocks of the physiology of the heart, and have been the subject of a vast number of interspecies studies in biomedical fields."]
This research project has been led by Nicholas Smith, an assistant professor working in the Laboratory for Scientific Instrumentation and Engineering (LaSIE) of the Department of Applied Physics at Osaka University. He was supervised by Satoshi Kawata, director of LaSIE and professor at both the Department of Applied Physics and the School of Frontier Biosciences. Here is a link to a page describing some of their research projects, Nano surgery and stimulation of living cells by ultrashort pulsed lasers.
Here is an excerpt from the OSA news release describing how this laser technology could be used in labs. "One potential application of this technology is in studying uncoordinated contractions in heart muscle. Normally, heart muscle contracts in a highly coordinated fashion, and this is what allows the heart to pump blood through the vasculature. But in some people, this coordinated beating breaks down, and the heart twitches irregularly -- a condition known as fibrillation. The new laser technique may allow scientists to create a form of fibrillation in the test tube. The lasers can destabilize the beating of the cells in laboratory experiments by introducing a beat frequency in one target cell distinct from the surrounding cells. This would allow scientists to study irregular heart beats on a cellular level and screen anti-fibrillation drugs."
For more information, this research work has been published online in Optics Express under the name "A femtosecond laser pacemaker for heart muscle cells" (Volume 16, Issue 12, Pages 8604-8616, June 2008). Here is the beginning of the abstract. "The intracellular effects of focused near-infrared femtosecond laser irradiation are shown to cause contraction in cultured neonatal rat cardiomyocytes. By periodic exposure to femtosecond laser pulse-trains, periodic contraction cycles in cardiomyocytes could be triggered, depleted, and synchronized with the laser periodicity. This was observed in isolated cells, and in small groups of cardiomyocytes with the laser acting as pacemaker for the entire group."
From this page, you'll get access to two short videos and to the text of the full article, from which the above illustration has been extracted. (PDF format, 13 pages, 836 KB). Unfortunately, there is not a single permanent link to this document.
Here is a first excerpt of the conclusions of the researchers. "In conclusion, we have shown that focused femtosecond laser irradiation of 15 to 30 mW power can be used to trigger contraction in individual heart muscle cells, and the contractions can be synchronized to the periodic application of laser light, allowing the laser to be used as an optical pacemaker. The pacemaking effect was also observed in groups of cells, even where only one cell in the group was targeted by the laser, showing that the periodic laser exposure can play an integral role in the dynamics of coupled and synchronized groups of cells."
The researchers also write that this technique could be used to synchronize contractions in heart muscle cells. "Although there are other simpler methods by which to synchronize cardiomyocytes (e.g. electrical current-based regulation of contraction or even photolysis of loaded caged compounds), the femtosecond laser interaction may be a useful tool with which to apply a driving stimulus that can synchronize contractions in heart muscle cells and may possibly be able to penetrate through substantial depths of heart muscle tissue due to the multiphoton absorption and may facilitate the investigation of such synchronization in-vivo, where other methods cannot be used or cannot achieve the same degree of subcellular localization."
As current pacemakers are doing correctly their jobs for many people, I'm not sure that an optical pacemaker using lasers will appear one day on the medical market. But I can be wrong...
Sources: Optical Society of America news release, May 28, 2008; and various websites
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