AJP - Cell Physiology, Vol 258, Issue 1 C179-C184, Copyright © 1990 by American Physiological Society

ARTICLES

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

G. Schmalzing, P. Eckard, S. Kroner and H. Passow
Max-Planck-Institut fur Biophysik, Frankfurt, Federal Republic of Germany.

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.

This article has been cited by other articles:

				M. Cereijido, R. G. Contreras, and L. Shoshani Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans Physiol Rev, October 1, 2004; 84(4): 1229 - 1262. [Abstract] [Full Text] [PDF]

				A. V. Chibalin, G. Ogimoto, C. H. Pedemonte, T. A. Pressley, A. I. Katz, E. Feraille, P.-O. Berggren, and A. M. Bertorello Dopamine-induced Endocytosis of Na+,K+-ATPase Is Initiated by Phosphorylation of Ser-18 in the Rat alpha  Subunit and Is Responsible for the Decreased Activity in Epithelial Cells J. Biol. Chem., January 22, 1999; 274(4): 1920 - 1927. [Abstract] [Full Text] [PDF]

				A. V. Chibalin, A. I. Katz, P.-O. Berggren, and A. M. Bertorello Receptor-mediated inhibition of renal Na+-K+-ATPase is associated with endocytosis of its alpha - and beta -subunits Am J Physiol Cell Physiol, November 1, 1997; 273(5): C1458 - C1465. [Abstract] [Full Text] [PDF]

				K. Machaca and S. Haun Store-operated Calcium Entry Inactivates at the Germinal Vesicle Breakdown Stage of Xenopus Meiosis J. Biol. Chem., December 1, 2000; 275(49): 38710 - 38715. [Abstract] [Full Text] [PDF]

				K. Machaca and S. Haun Induction of maturation-promoting factor during Xenopus oocyte maturation uncouples Ca2+ store depletion from store-operated Ca2+ entry J. Cell Biol., January 7, 2002; 156(1): 75 - 86. [Abstract] [Full Text] [PDF]