EXPRESSION OF MU-OPIATE RECEPTOR IN HUMAN EPIDERMIS AND KERATINOCYTES

There is increasing evidence that neurotransmitters play a crucial rol e in skin physiology and pathology, The expression and production of p roopiomelanocortin molecules such as beta-endorphin in human epidermis suggest that an opiate receptor is present in keratinocytes. In this paper we show that human epidermal keratinocytes express a mu-opiate r eceptor on both the mRNA level and the protein level. Performing polym erase chain reaction with cDNA libraries from human epidermal keratino cytes gave the polymerase chain reaction products of the expected leng th, which were confirmed as mu-opiate receptors by Southern blot analy sis. Using in situ hybridization techniques with a specific probe for mu-opiate receptors we detected the receptor in human epidermis, There was a cytoplasmic expression in all layers of the epidermis, which wa s more distinct in the suprabasal layers. Immunohistochemistry using t he mu-opiate receptor-specific antibody indicates that epidermis expre sses protein as well, and that the protein level is more elevated in t he basal layer. The correlation between the locations of both mRNA and protein expression in skin indicates that the mu-opiate receptor has not only been transcribed but also has a specific function, To prove a function of the receptor we performed a functional assay using skin o rgan cultures from human skin transplants. After 48 h incubation with Naloxone or beta-endorphin the expression of the mu-opiate receptor in epidermis was significantly downregulated compared with the control. These results show that a functional receptor indeed exists in human e pidermis.