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Expression of Mg 2+ ‐dependent, HCO 3 – ‐stimulated adenine triphosphatase in the human duodenum
Author(s) -
KONNO YUTAKA,
KATO KATSUAKI,
DAIRAKU NAOHIRO,
KOIKE TOMOYUKI,
IIJIMA KATSUNORI,
IMATANI AKIRA,
SEKINE HITOSHI,
OHARA SHUICHI,
SHIMOSEGAWA TOORU
Publication year - 2004
Publication title -
journal of gastroenterology and hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.214
H-Index - 130
eISSN - 1440-1746
pISSN - 0815-9319
DOI - 10.1111/j.1440-1746.2004.03175.x
Subject(s) - duodenum , medicine , microbiology and biotechnology , radiochemistry , biophysics , biology , chemistry
Background and Aim: Mg 2+ ‐dependent, HCO 3 – ‐stimulated adenine triphosphatase (Mg 2+ ‐HCO 3 – ‐ATPase) is an enzyme that catabolizes ATP in the presence of HCO 3 – and Mg 2+ . 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 Mg 2+ ‐HCO 3 – ‐ATPase in the human duodenum. Methods: The histochemistry of Mg 2+ ‐HCO 3 – ‐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 Mg 2+ ‐HCO 3 – ‐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 Mg 2+ ‐HCO 3 – ‐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 MgCl 2 and 50 mmol/L NaHCO 3 , but the activity was undetectable in pH <7.4 or >9.5. Conclusion: The results of the present study suggested that Mg 2 + ‐HCO 3 – ‐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.