LOCALIZATION OF HISTAMINE N-METHYLTRANSFERASE MESSENGER-RNA IN HUMAN NASAL-MUCOSA

Background: Histamine is metabolized mainly by histamine N-methyltrans ferase (HMT) to N-tau-methylhistamine in human nasal mucosa. Human HMT cDNA has been cloned and expressed in COS cells. The purpose of this study was to determine the localization of HMT mRNA in human nasal muc osa. Methods: The fragment (nucleotide residues 430-1055) of human HMT cDNA was subcloned in a Bluescript vector (Stratagene, La Jolla, Cali f.), and HMT sense and anti-sense RNA probes were made with T-7 and T- 3 RNA polymerases. In situ hybridization with digoxigenin-labeled RNA probes was performed on surgical specimens of human nasal turbinates. Results: HMT mRNA was localized in cells in the epithelium and submuco sa, and densely in endothelial cells of vessels. No HMT mRNA was ident ified in the submucosal glands. The presence of HMT mRNA was confirmed by Northern blot analysis, and HMT activities were also detected in n asal mucosa. Conclusion: Our study indicates that endothelium expresse s HMT mRNA, whereas cells in the epithelium and submucosa, which remai n unidentified, are on additional source of HMT mRNA.