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Membrane adenosine triphosphatase activities in rat pancreas
Biochimica Et Biophysica Acta
|November 4, 1980
Summary
Researchers investigated ATPase enzymes in rat pancreas for bicarbonate secretion. They found mitochondrial ATPase, not a plasma membrane bicarbonate-ATPase, is responsible. A distinct plasma membrane Ca2+/Mg2+-ATPase was identified with high activity.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Understanding the role of membrane ATPase enzymes in pancreatic bicarbonate (HCO3-) secretion is crucial for deciphering exocrine pancreatic function.
- Previous hypotheses suggested a plasma membrane bicarbonate-ATPase might be involved in HCO3- transport.
- Investigating specific ATPase activities in pancreatic membrane fractions is key to identifying their physiological roles.
Purpose of the Study:
- To investigate the involvement of membrane ATPase activities in rat pancreatic HCO3- secretion.
- To characterize the properties of identified ATPase activities, particularly in plasma membrane fractions.
- To determine if a distinct plasma membrane bicarbonate-ATPase exists and contributes to pancreatic secretion.
Main Methods:
- Fractionation of rat pancreatic membranes via sucrose density gradients.
- Assay of various ATPase activities (e.g., Mg2+-ATPase, Ca2+-ATPase, Na+/K+-ATPase, mitochondrial ATPase) in isolated membrane fractions.
- Characterization of a novel plasma membrane ATPase using inhibitors (p-fluorosulfonylbenzoyladenosine) and assessment of its properties (e.g., dependence on divalent cations, vanadate insensitivity).
Main Results:
- All HCO3(-)-sensitive ATPase activity was attributed to pancreatic mitochondrial ATPase, refuting the presence of a plasma membrane bicarbonate-ATPase in pancreatic secretion.
- A high-activity Mg2+- and Ca2+-requiring ATPase, distinct from known ATPases (Na+/K+-ATPase, Ca2+-ATPase, H+-ATPases), was identified in the plasma membrane fraction.
- This novel plasma membrane (Ca2+ + Mg2+)-ATPase was characterized, showing inhibition by p-fluorosulfonylbenzoyladenosine and covalent labeling of a ~35,000 Mr protein.
Conclusions:
- The study concludes that pancreatic mitochondrial ATPase, not a plasma membrane bicarbonate-ATPase, accounts for HCO3(-)-sensitive ATPase activity in the pancreas.
- A novel, high-activity (Ca2+ + Mg2+)-ATPase in the plasma membrane was identified and characterized, suggesting a potential, yet undefined, role in cellular processes.
- No direct candidate for an ATPase involved in ion transport at the luminal surface of pancreatic cells was found, but attention is directed to the plasma membrane (Ca2+ + Mg2+)-ATPase.