當(dāng)你走到太陽(yáng)下,，感受陽(yáng)光的不只是你的雙眼。你的皮膚也與視網(wǎng)膜一樣含有光感受器,，從而能夠迅速對(duì)有害的紫外線輻射采取防御,。 皮膚通過(guò)產(chǎn)生黑色素而變黑,，黑色素可以保護(hù)DNA不受紫外線的損傷。我們已經(jīng)知道,，在被太陽(yáng)暴曬幾天后,，陽(yáng)光中的UVB紫外線才會(huì)使皮膚增加黑色素的產(chǎn)生，以應(yīng)對(duì)皮膚中的DNA損傷,。但是,，陽(yáng)光中的UVA紫外線卻可以在幾分鐘內(nèi)就促進(jìn)黑色素的產(chǎn)生。 布朗大學(xué)的埃琳娜·萬(wàn)恰和同事認(rèn)為他們知道其中的原因,。他們分析了負(fù)責(zé)生產(chǎn)黑色素的黑素細(xì)胞的基因表達(dá),，發(fā)現(xiàn)這些細(xì)胞也能產(chǎn)生視紫紅質(zhì)，即存在于視網(wǎng)膜中的光敏物質(zhì),。 當(dāng)研究小組用UVA紫外線照射黑素細(xì)胞時(shí),，他們發(fā)現(xiàn)黑色素分泌量有所上升。在24小時(shí)內(nèi),，黑色素的分泌增加了4倍,。而去掉黑素細(xì)胞中負(fù)責(zé)分泌視紫紅質(zhì)的基因，也就阻斷了其對(duì) UVA紫外線的這種即刻反應(yīng)能力,。萬(wàn)恰認(rèn)為,，這種即刻“變黑”的過(guò)程盡管不那么明顯，卻可以幫助保護(hù)皮膚抵御早期的DNA受損,。 不過(guò),，澳大利亞昆士蘭大學(xué)的里克·斯特姆并不相信皮膚“看到”陽(yáng)光的功能可以使之獲得很大程度的保護(hù)。他說(shuō)：“即刻變黑并不能抵御紫外線引起的曬傷或DNA損傷,?！?(生物谷 Bioon.com) doi:10.1016/j.cub.2011.09.047 PMC: PMID: UVA Phototransduction Drives Early Melanin Synthesis in Human Melanocytes Nadine L. Wicks, Jason W. Chan, Julia A. Najera, Jonathan M. Ciriello, Elena Oancea Exposure of human skin to solar ultraviolet radiation (UVR), a powerful carcinogencomprising 95% ultraviolet A (UVA) and 5% ultraviolet B (UVB) at the Earth's surface, promotes melanin synthesis in epidermal melanocytes , which protects skin from DNA damage . UVB causes DNA lesions that lead to transcriptional activation of melanin-producing enzymes, resulting in delayed skin pigmentation within days . In contrast, UVA causes primarily oxidative damage and leads to immediate pigment darkening (IPD) within minutes, via an unknown mechanism . No receptor protein directly mediating phototransduction in skin has been identified. Here we demonstrate that exposure of primary human epidermal melanocytes (HEMs) to UVA causes calcium mobilization and early melanin synthesis. Calcium responses were abolished by treatment with G protein or phospholipase C (PLC) inhibitors or by depletion of intracellular calcium stores. We show that the visual photopigment rhodopsin is expressed in HEMs and contributes to UVR phototransduction. Upon UVR exposure, significant melanin production was measured within one hour; cellular melanin continued to increase in a retinal- and calcium-dependent manner up to 5-fold after 24 hr. 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. P>