title: Novel bumetanide-sensitive K+ transport in preimplantation mouse conceptuses.
abstract: Ouabain-resistant K+ transport activity was characterized primarily by measuring Rb+ uptake because 86Rb+ has a more convenient half-life than 42K+. Ouabain-resistant 86Rb+ uptake by mouse two-cell conceptuses and blastocysts was slowed by the K(+)-Na(+)-2Cl- cotransporter inhibitors bumetanide [inhibitory constant (Ki) = 400 nM] and furosemide (Ki approximately 10 microM), but it was insensitive to a variety of K+ channel blockers. This component of 86Rb+ transport was also inhibited by K+ and nonradioactive Rb+ and it was stimulated by Cl-. Nevertheless, neither 36Cl- nor 22Na+ uptake was inhibited by bumetanide, whereas 42K+ uptake was inhibited by both bumetanide and furosemide. Bumetanide-sensitive Rb+ transport in blastocysts had a Hill coefficient of 1.0 and a Michaelis constant value of 3.0 mM. By these criteria, preimplantation conceptuses contain a novel, bumetanide-sensitive K+ transport system that does not cotransport Cl- or Na+. Moreover, bumetanide-sensitive Rb+ uptake was 10 times faster in blastocysts when they were collapsed to expose the basal membrane of the trophectoderm to 86Rb+ in the medium. Therefore, the novel system may be located predominantly in the basal rather than in the apical membrane of the trophectoderm.
authors.affiliation: Department of Biochemistry, Chicago College of Osteopathic Medicine, Downers Grove, Illinois 60515.
authors.forename: L J
authors.initials: LJ
authors.lastname: Van Winkle
authors.forename: A L
authors.initials: AL
authors.lastname: Campione
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001755:Blastocyst / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology*; D002712:Chlorides / Q000493:pharmacokinetics / Q000502:physiology; D007700:Kinetics; D051379:Mice; D008813:Mice, Inbred ICR; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000493:pharmacokinetics
chemical_list: D000596:Amino Acids; D002712:Chlorides; D002034:Bumetanide; D010042:Ouabain; D012413:Rubidium; D011188:Potassium