title: Specific binding of progesterone to the cell surface and its role in the meiotic divisions in Rana oocytes.
abstract: Progesterone is believed to act at the cell surface to induce the resumption of the meiotic divisions in amphibian oocytes. Analysis of [3H]- and [14C] progesterone uptake and exchange by the plasma-vitelline membrane complex, nucleus and cytoplasm of the isolated Rana oocyte indicates that progesterone uptake by the plasma membrane is saturable, specific and temperature-dependent, and has a slow off-rate. Estradiol (a noninducer) did not compete with progesterone, whereas testosterone (an inducer) blocked progesterone uptake by the membrane complex. Scatchard-type plots indicate an apparent Kd of 5.1.10-7 M over the [progesterone]0 range of 0.01-1.0 microM with maximum binding at about 70 fmol per oocyte. Membrane uptake at higher [progesterone]0 (2-40 microM) indicates apparent cooperative binding, with saturation up to 10 pmol per oocyte. Cytoplasmic uptake was apparently nonspecific and less temperature-dependent than membrane uptake and steroid concentrations (progesterone and pregnanediones) exceeded water solubility by 30-60 min. Nuclear uptake was saturable and specific but uptake was independent of temperature. A comparison of membrane binding and a physiological response (nuclear breakdown) indicated only about 10% of the membrane sites need be filled to initiate a 50% response.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008540:Meiosis; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000378:metabolism; D010063:Ovum / Q000502:physiology*; D011374:Progesterone / Q000378:metabolism* / Q000494:pharmacology; D011894:Rana pipiens; D011980:Receptors, Progesterone / Q000378:metabolism*; D013739:Testosterone / Q000494:pharmacology; D014817:Vitelline Membrane / Q000378:metabolism
chemical_list: D011980:Receptors, Progesterone; D013739:Testosterone; D011374:Progesterone; D010042:Ouabain