A blood vessel receptor that responds to light could aid more effective treatment of vascular diseases and other medical conditions. A team led by Johns Hopkins Medicine discovered the receptor, which causes blood vessels to relax in response to light. The researchers also found that blood vessel function can be regulated through changing light wavelengths. The researchers made the findings inadvertently when their blood-vessel-analysis equipment revealed tension in vessels after motion detection lights came on. “I had this slightly crazy idea,” said professor Dr. Dan Berkowitz. “What if there were receptors for light on blood vessels? Perhaps blood vessels could ‘see’ the light or ‘had eyes.’” The researchers looked for expression of a light receptor in the blood vessels of mice. They discovered melanopsin (opsin 4), which exists in a group of nonimage-forming receptors. In those without opsin 4, the blood vessels did not relax in response to light. The team determined the exact wavelength at which opsin 4 is activated and blood vessel relaxation response is maximal. Wavelength-specific light was used to increase blood flow in the tails of normal mice, but not in the ones that lacked expression of opsin 4. The team’s “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,” said Dr. Zorina Galis, chief of vascular biology and hypertension at the National Heart, Lung and Blood Institute. It will be important to determine if this phenomenon is present across all species and in all vascular beds, too, according to the researchers. They also hope to uncover all of the signaling and regulatory mechanisms that are linked to the light receptor. A variety of medical applications could be possible, including the use of opsin 4 to treat ailments such as Raynaud’s phenomenon, which is characterized by exaggerated vasoconstriction of the vessels of the fingers and toes. “We plan to use high-intensity ... LEDs incorporated into gloves as a potential mode of therapy for these patients,” Berkowitz said. “Additionally, socks with LEDs could be used in diabetic patients to potentially enhance blood flow and heal chronic ischemic ulcers.” The research was published in the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1420258111). For more information, visit www.hopkinsmedicine.org.