AJP - Cell Physiology, Vol 263, Issue 4 C773-C779, Copyright © 1992 by American Physiological Society
Novel bumetanide-sensitive K+ transport in preimplantation mouse conceptuses
L. J. Van Winkle and A. L. Campione
Department of Biochemistry, Chicago College of Osteopathic Medicine, Downers Grove, Illinois 60515.
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.
