



Video: Laser-controlled heart

What makes your pulse quicken? For the millimetre-size hearts quail embryos, a laser does the trick. Experiments show that an infrared laser can control the pace of the tiny hearts – the first time that a laser has been shown to affect a whole heart in a living organism.

We already knew that light can stimulate nerve activity, and two years ago Nicholas Smith at Osaka University, Japan, showed that 8-millisecond bursts of 80-femtosecond laser pulses could synchronise the pulsing of heart cells in culture. But now a team led by Andrew Rollins at Case Western Reserve University in Cleveland, Ohio, has used a different type of laser to trigger beats across an entire vertebrate heart – albeit a tiny one – in a living organism.

Rollins’s group piped millisecond-long pulses of infrared laser light with a wavelength of 1.87 micrometres through an optical fibre, which ended just 500 micrometres from the embryo. Before they switched on the laser, the heart beat once every 1.5 seconds, but firing the laser twice a second quickened the heartbeat to match the laser rate as long as the laser fired (see video, above).


“It worked beautifully: the heart rate was in lockstep with the laser pulse rate,” says Duco Jansen of Vanderbilt University in Nashville, Tennessee, who collaborated with Rollins on the experiments. The team saw no sign of laser damage after hours of experiments – although prepping the heart for the experiment involved opening the egg, which ultimately killed the embryo.

Jansen picked the 1.87-micrometre wavelength because water partly absorbs such light, warming cells but not cooking them. Somehow the temperature gradient triggers the changes in membrane potential that make the heart beat.

Electricity off

Early applications of the technique will be in studying the developing heart to illuminate cardiac disease – particularly in probing embryonic hearts that are too small to have electrodes inserted into them. “This is an alternative to electrical stimulation with higher spatial resolution,” says Jansen. “And since we’re stimulating in a domain different than the electrical domain in which we’re recording data, it avoids interference.”

He adds that better understanding of the excitation mechanisms will be critical in building devices for use in clinical applications, which could include optical pacemakers.

Smith, who was not involved in the research, is impressed, calling it “a significant advance in optical pacing and in using light to modify and control living systems that would not be thought to respond to light”. He hopes to see more work on heating and optical damage, and on optical control of other biological functions.

Journal reference: Nature Photonics, DOI: 10.1038/nphoton.2010.166