3D microscopy technique allows scientists to trace dangerous heart waves

A pioneering 3D imaging method has been applied to heart cells for the first time, allowing researchers to trace waves that can cause arrhythmia.

Rising levels of calcium in heart muscle cells cause contraction of the muscle, helping to regulate the beating of the heart. The rise in calcium levels is usually uniform, but sometimes there is a spontaneous release of calcium from isolated regions of the cells, creating a wave of calcium.

The video at the top of the page shows three regular calcium releases in a heart cell triggered by an external electrical pacing, followed by two spontaneous calcium waves.

These waves can cause arrhythmia, the irregular beating of the heart. Arrhythmia accounts for approximately 50 percent of deaths in patients with heart failure.

However, how and why calcium waves originate has been difficult to study with conventional microscopy techniques. Now, physicists from Imperial College London have collaborated with scientists from Imperial’s National Heart and Lung Institute (NHLI) to shine a new kind of light on the problem.

Their results, published this week in the Journal of Biophotonics, reveal initial findings that calcium waves originate from healthy parts of heart muscle cells, and not degraded regions as the researchers had expected.

Shedding light

The technique, called oblique plane microscopy (OPM), was invented by physicists in Imperial’s Photonics group. In order to study cells in 3D, scientists most commonly use confocal microscopy, which looks at one point on the sample at a time.

OPM looks at a layer of the sample at a time instead of a point, and combines this with a method to rapidly sweep the layer being imaged through the specimen.

The video above shows a calcium wave propagating through layers of a heart cell.

This allows video-rate 3D imaging of features at the sub-cellular scale. This is particularly important for looking at calcium waves, since they are rare events and their point of origin within the cell is not known before it happens.

Using this technique, researchers at the NHLI investigated single heart muscle cells isolated from a rat model of heart failure.

Surprise result

Within heart muscle cells, there are structures in the cell membrane called transverse tubules or t-tubules, which are essential for normal calcium release. In patients with heart failure, the structure of t-tubules is degraded.

The researchers had speculated that these faulty structures were the origin of calcium waves, but when they looked at the microscopy data, the opposite pattern emerged.

Calcium waves were more frequent from regions of the cell where the normal t-tubule structure was preserved. “We thought more calcium waves would be produced from regions of deranged t-tubules, but we were surprised to find the opposite appears to be true,” said Dr Ken MacLeod of the NHLI, a lead researcher on the project.

“However, this was only a small-scale study to test the technique. We still expect the derangement of t-tubules plays a role in the poor function of failing cells, and hopefully with more research we should be able to see what’s going on in greater detail. Knowing more about the origin of calcium waves would be an important first step in combatting arrhythmia.”

Dr Chris Dunsby of the Department of Physics and Centre for Pathology at Imperial and a lead researcher on the project said: “Now we have proven OPM can give real insights into these processes, we hope to improve the technique and continue working with the NHLI.

“OPM could be applied to many more problems in biology in the future, such as signalling in neurons and rapid 3D imaging of large arrays of samples, for example for drug screening.”

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'High speed sCMOS-based oblique plane microscopy applied to the study of calcium dynamics in cardiac myocytes' by Markus B. Sikkel, Sunil Kumar, Vincent Maioli, Christina Rowlands, Fabiana Gordon, Sian E. Harding, Alexander R. Lyon, Kenneth T. MacLeod andChris Dunsby is published in the Journal of Biophotonics.