title: Expression of Mg2+-dependent, HCO3- -stimulated adenine triphosphatase in the human duodenum.
abstract: OBJECTIVE
  Mg2+-dependent, HCO3- -stimulated adenine triphosphatase (Mg2+-HCO3- -ATPase) is an enzyme that catabolizes ATP in the presence of HCO3- and Mg2+. The activity of this ATPase is known to be present in the duodenum, but its physiological role remains unclear. In the present study, the aim was to study the distribution and biochemical profiles of Mg2+-HCO3- -ATPase in the human duodenum.
  
  
  METHODS
  The histochemistry of Mg2+-HCO3- -ATPase, its localization using electron microscopy (EMS), and the measurement of enzyme activity were carried out by using mucosal samples of the bulb, and the second and third portions of the duodenum, obtained from six volunteers by endoscopic biopsy.
  
  
  RESULTS
  The Mg2+-HCO3- -ATPase was detected in the brush border along the luminal surface of human duodenal epithelial cells. The EMS confirmed its localization to the surface of microvilli. The activity of Mg2+-HCO3- -ATPase was higher in the distal portions of the human duodenum than in the bulb. Its maximal activity was obtained under a pH of 8.5, and in the presence of 1.0 mmol/L MgCl2 and 50 mmol/L NaHCO3, but the activity was undetectable in pH <7.4 or >9.5.
  
  
  CONCLUSIONS
  The results of the present study suggested that Mg2+-HCO3- -ATPase may work for luminal alkalization in the distal portions of the human duodenum and may contribute to maintaining the activity of pancreatic digestive enzymes.
authors.affiliation: Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Konno
authors.forename: Katsuaki
authors.initials: K
authors.lastname: Kato
authors.forename: Naohiro
authors.initials: N
authors.lastname: Dairaku
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Koike
authors.forename: Katsunori
authors.initials: K
authors.lastname: Iijima
authors.forename: Akira
authors.initials: A
authors.lastname: Imatani
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sekine
authors.forename: Shuichi
authors.initials: S
authors.lastname: Ohara
authors.forename: Tooru
authors.initials: T
authors.lastname: Shimosegawa
mesh_terms: D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism* / Q000648:ultrastructure; D016099:Endoscopy, Gastrointestinal; D006801:Humans; D016018:Least-Squares Analysis; D008854:Microscopy, Electron
chemical_list: D017301:Ca(2+) Mg(2+)-ATPase