Monday, November 7, 2011 (Last Updated: 11/08/2011)
MONDAY, Nov. 7 (HealthDay News) -- Immediate pigment darkening (IPD) may occur via a novel ultraviolet (UV) A signaling pathway involving calcium mobilization and early melanin synthesis in human epidermal melanocytes (HEMs), with the photopigment rhodopsin, which is expressed in HEMs, contributing to phototransduction, according to a study published online Nov. 3 in Current Biology.
Nadine L. Wicks, from Brown University in Providence, R.I., and colleagues sought to identify the receptor protein which directly mediates UVA related phototransduction in skin, and to investigate the effect of UVA exposure on HEMs. To understand the mechanism of IPD, they designed a system that permitted real-time imaging of cultured cells, and simultaneous exposure to irradiation that was comparable to UV radiation.
The investigators found that exposure of HEMs to UVA resulted in mobilization of calcium, and early synthesis of melanin. Depletion of the intracellular calcium store or treatment with G protein or phospholipase C inhibitors abolished calcium responses. Rhodopsin was found to be expressed in HEMs, and contributed to UV radiation phototransduction. Significant melanin production occurred within one hour of exposure to UV radiation. After 24 hours of exposure, melanin production continued to increase five-fold in a retinal and calcium dependent manner.
"Our findings identify a novel UVA-sensitive signaling pathway in melanocytes that leads to calcium mobilization and melanin synthesis and may underlie the mechanism of IPD in human skin," the authors write.
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