title: Regulatory changes of membrane transport and ouabain binding during progesterone-induced maturation of Xenopus oocytes.
abstract: During progesterone-stimulated maturation of defolliculated full-grown Xenopus oocytes, the activities of the transport systems for L-alanine, thymidine, chloride, phosphate, and alkali ions decrease. Differences of the extent and time course of these changes suggest that they are controlled by at least partially independent mechanisms. A closer investigation of the Na-K ATPase has shown that in unstimulated oocytes, ouabain produces maximal inhibition when 8-12 X 10(9) molecules are bound per cell. This number is bound during the first phase of a diphasic uptake process. Since this phase can be suppressed by increasing the concentration of external K+ to 45 mmol/liter or more, it is concluded that it refers to binding to the Na-K pump in the plasma membrane. Ouabain bound prior to progesterone-induced germinal vesicle breakdown (GVBD) remains bound after the breakdown, although the Na-K pump loses the capacity to bind ouabain after GVBD in oocytes that had not been exposed to ouabain preceding GVBD. In the presence of Mg++ membranes isolated before regulatory inhibition of pumping and ouabain binding show a Na+-dependent incorporation of 32P from gamma-[32P]-ATP that can be reversed by the addition of K+. The phosphorylation site migrates on LiDS-polyacrylamide gel electropherograms at about 98,000 daltons and can be identified as a Commassie blue-stainable band.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005260:Female; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology*; D011955:Receptors, Drug / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014981:Xenopus
chemical_list: D011955:Receptors, Drug; C028996:cardiac glycoside receptors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase