Blood vessels relax when they ‘see’ the light

"I had this slightly crazy idea," says Dan Berkowitz. "What if there were receptors for light on blood vessels? Perhaps blood vessels could 'see' the light or 'had eyes.'" (Credit: Lucas Cobb/Flickr)

Light can prod blood vessels to relax, a discovery that came about almost accidentally when researchers moved some gear into a room with motion-triggered lights.

They found that blood vessels in mice have a light-sensitive receptor that, when activated, causes arteries, veins, and capillaries to relax.

The scientists pinned down the exact light wavelength that activates the receptor. Using that wavelength, they were able to increase blood flow in the animals’ tails.

The study, which could lead to light-based therapies for conditions like Raynaud’s phenomenon, diabetes, and vascular ulcers, was published online by the Proceedings of the National Academy of Sciences.

“If we can develop novel ways of delivering light to blood vessels, this molecular switch for relaxation could be harnessed in all types of vascular disease treatment,” says senior author Dan Berkowitz, a Johns Hopkins University professor of anesthesiology/critical care medicine and biomedical engineering.

‘Slightly crazy idea’

The discovery by Berkowitz and his colleagues came about almost by accident. When their blood vessel analysis equipment was moved into a new room with energy-saving motion-activated lights, they noticed that blood vessel tension decreased when the lights turned on. The team decided to investigate.


They found that a similar discovery had been made in the 1950s. Berkowitz says, however, that the explanation the earlier researchers proposed seemed unlikely to him; he wanted to do further research.

“I had this slightly crazy idea,” he says. “What if there were receptors for light on blood vessels? Perhaps blood vessels could ‘see’ the light or ‘had eyes.'”

The researchers discovered a light receptor in mice blood vessels called melanopisn, or opsin 4, one of a group of receptors that sense light but do not contribute to forming a visual image. In mice without opsin 4, blood vessels did not relax in response to light.

Berkowitz and his team determined the exact wavelength at which opsin 4 is activated and blood vessel relaxation response is greatest. The scientists used wavelength-specific light to increase blood flow in the tails of normal mice; they did not get the same improvement in mice that lacked opsin 4.

“This group’s finding provides a perfect example of how following up on unexpected results can lead to important basic biomedical research discoveries,” says Zorina Galis, chief of the vascular biology and hypertension branch of the National Heart, Lung and Blood Institute. “In addition, their basic discovery now opens the way to investigations of whether wavelength-specific light stimulation of blood vessels might be used to manage a variety of medical conditions.”

A next step is to find out if light-induced vessel relaxation occurs across all species and in all areas of the circulatory system. Researchers also want to uncover signaling and regulatory mechanisms linked to the receptor. They will want to explore whether there are receptor problems in patients with vascular disease.

Berkowitz sees a variety of potential applications for his research. For example, his group hopes to use light to help patients with Raynaud’s phenomenon, an exaggerated vasoconstriction of the vessels that can lead to numbness and cold in the fingers and toes.

“We plan to use high-intensity light-emitting diodes, or LEDs, incorporated into gloves as a potential mode of therapy for these patients,” Berkowitz says. “Additionally, socks with LEDs could be used in diabetic patients to potentially enhance blood flow and heal chronic ischemic ulcers.”

The National Heart, Lung and Blood Institute, the National Institute of Mental Health, and the National Institute on Drug Abuse funded the study.

Source: Johns Hopkins University