AJP - Cell Physiology, Vol 262, Issue 6 C1520-C1530, Copyright © 1992 by American Physiological Society
Regulation of alpha 1-beta 3-NA(+)-K(+)-ATPase isozyme during meiotic maturation of Xenopus laevis oocytes
D. Pralong-Zamofing, Q. H. Yi, G. Schmalzing, P. Good and K. Geering
Institute of Pharmacology and Toxicology, University of Lausanne, Switzerland.
During progesterone-induced maturation of Xenopus oocytes, the transport
and ouabain binding capacity of Na(+)-K(+)-ATPase at the plasma membrane is
completely downregulated. To elucidate the mechanism and the physiological
significance of this process, we have followed the fate of oocyte
alpha-beta 3-Na(+)-K(+)-ATPase complexes during meiotic maturation and
early embryonic development. An immunocytochemical follow-up of the
catalytic alpha-subunit, ouabain binding studies, cell surface iodination,
and oocyte cell fractionation combined with immunochemical subunit
detection provides evidence that following progesterone treatment
Na(+)-K(+)-ATPase molecules are retrieved from the oocyte plasma membrane.
The enzyme complexes are recovered in an active form in an intracellular
compartment in both in vitro and in vivo matured eggs. Exogenous Xenopus
alpha 1- and beta 1-complexes expressed in the oocyte from injected cRNAs
are regulated by progesterone similar to endogenous Na(+)-K(+)-ATPase
complexes. Finally, active Na(+)-K+ pumps internalized during oocyte
maturation appear to be redistributed to plasma membrane fractions during
blastula formation in Xenopus embryos. In conclusion, our data suggest that
endocytosis of alpha 1- and beta 3-complexes during meiotic maturation of
Xenopus oocytes is responsible for downregulation of Na(+)-K(+)-ATPase
activity and results in an intracellular pool of functional enzymes, which
might be reexpressed during early development in response to physiological
needs.
