Expression of μ-opiate receptor in human epidermis and keratinocytes

There is increasing evidence thai neurotransmitters play a crucial role in skin physiology and pathology. The expression and production of proopiomelanocortin molecules such as β-endorphin in human epidermis suggest that an opiate receptor is present in keratinocytes. In this paper we show that human epidermal keratinocytes express a If-opiate receptor on both the mRNA level and the protein level. Performing polymerase chain reaction with cDNA libraries from human epidermal keratinocytes gave the polymerase chain reaction products of the expected length, which were confirmed as If-opiate receptots by Southern blot analysis. Using in situ hybridization techniques with a specific probe for μ-opiate receptors we detected the receptor in human epidermis. There was a cytoplasmic expression in all layers of the epidermis, which was more distinct in the suprabasal layers. Immunohistochemistry using the μ-opiate receptorspecific antibody indicates that epidermis expresses protein as well, and that the protein level is more elevated in the basal layer. The correlation between the locations of both mRNA and protein expression in skin indicates that the μf-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 organ cultures from human skin transplants. After 48 h incubation with Naloxone or β-endorphin the expression of the μ-opiate receptor in epidermis was significantly downregulated compared with the control. These results show that a functional receptor indeed exists in human epidermis.