Expression of Mg2+-dependent, HCO3- -stimulated adenine triphosphatase in the human duodenum.
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.
Konno
Yutaka
Y
Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.
Kato
Katsuaki
K
Dairaku
Naohiro
N
Koike
Tomoyuki
T
Iijima
Katsunori
K
Imatani
Akira
A
Sekine
Hitoshi
H
Ohara
Shuichi
S
Shimosegawa
Tooru
T
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
D017301:Ca(2+) Mg(2+)-ATPase