Downregulation of surface sodium pumps by endocytosis during meiotic maturation of Xenopus laevis oocytes
- Max-Planck-Institut fuer Biophysik, Frankfurt (Germany, F.R.)
During meiotic maturation, plasma membranes of Xenopus laevis oocytes completely lose the capacity to transport Na and K and to bind ouabain. To explore whether the downregulation might be due to an internalization of the sodium pump molecules, the intracellular binding of ouabain was determined. Selective permeabilization of the plasma membrane of mature oocytes (eggs) by digitonin almost failed to disclose ouabain binding sites. However, when the eggs were additionally treated with 0.02% sodium dodecyl sulfate (SDS) to permeabilize inner membranes, all sodium pumps present before maturation were recovered. Phosphorylation by (gamma-32P)ATP combined with SDS-polyacrylamide gel electrophoresis (PAGE) and autoradiography showed that sodium pumps were greatly reduced in isolated plasma membranes of eggs. According to sucrose gradient fractionation, maturation induced a shift of sodium pumps from the plasma membrane fraction to membranes of lower buoyant density with a protein composition different from that of the plasma membrane. Endocytosed sodium pumps identified on the sucrose gradient from (3H)ouabain bound to the cell surface before maturation could be phosphorylated with inorganic (32P)phosphate. The findings suggest that downregulation of sodium pumps during maturation is brought about by translocation of surface sodium pumps to an intracellular compartment, presumably endosomes. This contrasts the mechanism of downregulation of Na-dependent cotransport systems, the activities of which are reduced as a consequence of a maturation-induced depolarization of the membrane without a removal of the corresponding transporter from the plasma membrane.
- OSTI ID:
- 7025858
- Journal Information:
- American Journal of Physiology; (USA), Journal Name: American Journal of Physiology; (USA) Vol. 258; ISSN 0002-9513; ISSN AJPHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ACID ANHYDRASES
ALKALI METALS
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
ATP
ATP-ASE
AUTORADIOGRAPHY
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CARBOHYDRATES
CARDIAC GLYCOSIDES
CARDIOTONICS
CARDIOVASCULAR AGENTS
CELL CONSTITUENTS
CELL DIFFERENTIATION
CELL MEMBRANES
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTROPHORESIS
ELEMENTS
ENZYMES
FROGS
GERM CELLS
GLYCOSIDES
HOMEOSTASIS
HYDROGEN COMPOUNDS
HYDROLASES
ISOTOPES
KINETICS
LIGHT NUCLEI
MEMBRANE TRANSPORT
MEMBRANES
METALS
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
OOCYTES
ORGANIC COMPOUNDS
OUABAIN
OXYGEN COMPOUNDS
PERMEABILITY
PHOSPHATES
PHOSPHOHYDROLASES
PHOSPHORUS 32
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
POTASSIUM
RADIOISOTOPES
REACTION KINETICS
SODIUM
STROPHANTHINS
TRITIUM COMPOUNDS
VERTEBRATES