Downregulation of surface sodium pumps by endocytosis during meiotic maturation of Xenopus laevis oocytes

Journal Article · Mon Jan 01 00:00:00 EST 1990 · American Journal of Physiology; (USA)

OSTI ID:7025858

Schmalzing, G; Eckard, P; Kroener, S P; Passow, H ^[1]

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1. 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), Vol. 258; ISSN 0002-9513
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
OOCYTES
CELL DIFFERENTIATION
OUABAIN
BIOCHEMICAL REACTION KINETICS
POTASSIUM
MEMBRANE TRANSPORT
SODIUM
ATP
ATP-ASE
AUTORADIOGRAPHY
CELL MEMBRANES
ELECTROPHORESIS
FROGS
HOMEOSTASIS
PERMEABILITY
PHOSPHATES
PHOSPHORUS 32
TRITIUM COMPOUNDS
ACID ANHYDRASES
ALKALI METALS
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOHYDRATES
CARDIAC GLYCOSIDES
CARDIOTONICS
CARDIOVASCULAR AGENTS
CELL CONSTITUENTS
DAYS LIVING RADIOISOTOPES
DRUGS
ELEMENTS
ENZYMES
GERM CELLS
GLYCOSIDES
HYDROGEN COMPOUNDS
HYDROLASES
ISOTOPES
KINETICS
LIGHT NUCLEI
MEMBRANES
METALS
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHOHYDROLASES
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
RADIOISOTOPES
REACTION KINETICS
STROPHANTHINS
VERTEBRATES
551001* - Physiological Systems- Tracer Techniques