Photorelaxation or photo-vasorelaxation, is described as the relaxation of

blood vessel Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...

s in response to light. This has been reported for around sixty years, it was never described, pursued or explained. It was serendipitously rediscovered by Dr. Gautam Sikka and his mentor Dr. Dan Berkowitz at

Johns Hopkins University The Johns Hopkins University (often abbreviated as Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland, United States. Founded in 1876 based on the European research institution model, J ...

Baltimore Baltimore is the most populous city in the U.S. state of Maryland. With a population of 585,708 at the 2020 census and estimated at 568,271 in 2024, it is the 30th-most populous U.S. city. The Baltimore metropolitan area is the 20th-large ...

, USA, and along with his team he not only elucidated the mechanism but is trying to harness light for treatment of

cardiovascular disease Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases (e.g. angina, heart attack), heart failure, hypertensive heart disease, rheumati ...

. The research by Sikka ''et al'' concluded that there light-sensing receptors,

melanopsin Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinylidene protein, retinal proteins called opsins and encoded by the gene ''Opn4''. In the mammalian retina, there are two additional categories of opsins, b ...

receptors, are present in blood vessels and mediate wavelength specific, light-dependent vascular relaxation. This photorelaxation signal transduction involves

cyclic guanosine monophosphate Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP. Its most likely mechanism of action is activation of intracellular protein kinases in ...

(cGMP) and

phosphodiesterase A phosphodiesterase (PDE) is an enzyme that breaks a phosphodiester bond. Usually, ''phosphodiesterase'' refers to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below. However, there are many oth ...

type 6, but not cGMP-dependent protein

kinase In biochemistry, a kinase () is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule don ...

or Protein Kinase G (PKG). Furthermore, it is regulated by Beta adrenergic receptor kinase type 1 (βARK or BARK) also called G protein coupled receptor kinase 2 (GRK2), and involves vascular hyperpolarization, and this receptor pathway could be targeted for wavelength-specific light-based therapy in the treatment of diseases that involve altered vasoreactivity.

References

{{Reflist Angiology G protein-coupled receptors