title: Generation and subcellular distribution of histamine in human blood monocytes and monocyte subsets.
abstract: OBJECTIVE
  This study was designed to establish the sites of formation and storage of histamine and histidine decarboxylase (HDC) in human monocytes and two of their subsets.
  
  
  METHODS
  The experiments were carried out using monocytes from buffy coats of healthy blood donors. Histamine was quantitated by RIA, HDC activity by the formation of histamine.
  
  
  RESULTS
  The monocyte subtype RM3/1 contained significantly more histamine than the subset 27E10 (0.041+/-0.025 vs. 0.005+/-0.004 pg/cell, p < 0.05) and also more HDC activity and HDC mRNA. After fractionation of monocyte homogenates in a discontinuous Percoll gradient or by differential centrifugation more than 80% of both, HDC activity and histamine, were recovered from the cytosolic fractions. About 50% of this histamine was found to be bound to proteins.
  
  
  CONCLUSIONS
  In monocytes histamine and HDC are colocalized in the cytoplasm indicating a subcellular distribution different from mast cells or basophils. The data also show that histamine is synthesized by the monocytes themselves.
authors.affiliation: Institut für Pharmakologie und Toxikologie, Medizinische Fakultät der RWTH Aachen, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Zwadlo-Klarwasser
authors.forename: M
authors.initials: M
authors.lastname: Vogts
authors.forename: W
authors.initials: W
authors.lastname: Hamann
authors.forename: K
authors.initials: K
authors.lastname: Belke
authors.forename: J
authors.initials: J
authors.lastname: Baron
authors.forename: W
authors.initials: W
authors.lastname: Schmutzler
mesh_terms: D002458:Cell Fractionation; D002462:Cell Membrane / Q000737:chemistry; D003600:Cytosol / Q000737:chemistry; D006632:Histamine / Q000097:blood*; D006640:Histidine Decarboxylase / Q000097:blood / Q000235:genetics; D006801:Humans; D008861:Microsomes / Q000737:chemistry; D009000:Monocytes / Q000378:metabolism* / Q000648:ultrastructure*; D011485:Protein Binding; D012333:RNA, Messenger / Q000097:blood
chemical_list: D012333:RNA, Messenger; D006632:Histamine; D006640:Histidine Decarboxylase