Scientists at the University of Bonn have brought new meaning to the phrase "light-hearted" with the discovery of a way to cause arrhythmia in the heart cells of mice using only blue light and a sensor in the cell wall. It's hoped the method can be used to research the development of arrhythmia, one of the most common causes of death after a heart attack.
Mice were genetically modified to express channelrhodopsin proteins, which can be used as a light sensor and act as an ion channel in the cell membrane. When stimulated with blue light, the channel opens and positive ions flow into the cell which causes a change in the cell membrane pressure and the cardiac muscle cells contract.
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Tobias Brügmann, and his colleagues at the Institute for Physiology I at the University Of Bonn, hope this new method will open up new possibilities for researching the development of arrhythmia as it allows them to target very specific areas of the heart, even just a few cells, and find out which areas are especially sensitive to electric disruptions.
The approach "allowed us to change the electric potential of the mouse heart at will, enabling us to selectively produce conditions such as arrhythmia of the atrium or the ventricle,” explained Professor Dr. Bernd Fleischmann.
Arrhythmia, known also as ventricular fibrillation, is caused when large numbers of cardiac cells die and are replaced instead of connective scar tissue. “This scar tissue has a different electrical activity than the healthy heart muscle,” says the leader of the study, Professor Dr. Philipp Sasse. “And that makes the heart stumble.” Normally electrical impulses fan out across the heart forming a coordinated contraction, but if any muscles electrically uncouple they begin pulsing at their own rhythm causing the blood flow to arrest.
Heart attacks cause permanent tissue damage and for this reason increase the chance of arrhythmia, among the commonest causes of death after a heart attack. Until now research has relied on stimulation with electrodes to study the heart muscle in arrhythmia but with limited use as electrical stimulation longer than a few milliseconds causes toxic gases and a change in pH value. In contrast photostimulation can be applied for several minutes without problems.