Half of the (Na+ + K+)-transporting-ATPase-associated K+-stimulated p-nitrophenyl phosphatase activity of gastric epithelial cells is exposed to the surface exterior

Biochem J. 1988 May 15;252(1):29-34. doi: 10.1042/bj2520029.

Abstract

Ouabain inhibited 86RbCl uptake by 80% in rabbit gastric superficial epithelial cells (SEC), revealing the presence of a functional Na+,K+-ATPase [(Na+ + K+)-transporting ATPase] pump. Intact SEC were used to study the ouabain-sensitive Na+,K+-ATPase and K+-pNPPase (K+-stimulated p-nitrophenyl phosphatase) activities before and after lysis. Intact SEC showed no Na+,K+-ATPase and insignificant Mg2+-ATPase activity. However, appreciable K+-pNPPase activity sensitive to ouabain inhibition was demonstrated by localizing its activity to the cell-surface exterior. The lysed SEC, on the other hand, demonstrated both ouabain-sensitive Na+,K+-ATPase and K+-pNPPase activities. Thus the ATP-hydrolytic site of Na+,K+-ATPase faces exclusively the cytosol, whereas the associated K+-pNPPase is distributed equally across the plasma membrane. The study suggests that the cell-exterior-located K+-pNPPase can be used as a convenient and reliable 'in situ' marker for the functional Na+,K+-ATPase system of various isolated cells under noninvasive conditions.

MeSH terms

  • 4-Nitrophenylphosphatase / antagonists & inhibitors
  • 4-Nitrophenylphosphatase / metabolism*
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Dextrans / pharmacology
  • Epithelial Cells
  • Epithelium / enzymology
  • Furosemide / pharmacology
  • Gastric Mucosa / drug effects
  • Gastric Mucosa / enzymology*
  • In Vitro Techniques
  • Nitrophenols / pharmacology
  • Organophosphorus Compounds / pharmacology
  • Ouabain / pharmacology
  • Phosphoric Monoester Hydrolases / metabolism*
  • Polysaccharides / pharmacology
  • Potassium / pharmacology
  • Rabbits
  • Rubidium Radioisotopes
  • Sodium-Potassium-Exchanging ATPase / metabolism*

Substances

  • Dextrans
  • Nitrophenols
  • Organophosphorus Compounds
  • Polysaccharides
  • Rubidium Radioisotopes
  • nitrophenylphosphate
  • Ouabain
  • Furosemide
  • Adenosine Triphosphate
  • Phosphoric Monoester Hydrolases
  • 4-Nitrophenylphosphatase
  • Sodium-Potassium-Exchanging ATPase
  • Potassium