Ouabain-sensitive Rb + uptake in mouse eggs and preimplantation conceptuses
The results of histochemical and immunocytochemical studies have been used elsewhere to support the hypothesis that Na + K + - ATPase expression is initiated or increases dramatically in preimplantation mouse conceptuses just before they begin to cavitate. Moreover, localization of the enzyme in the...
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Veröffentlicht in: | Developmental biology 1991-07, Vol.146 (1), p.158-166 |
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Zusammenfassung: | The results of histochemical and immunocytochemical studies have been used elsewhere to support the hypothesis that
Na
+
K
+
-
ATPase
expression is initiated or increases dramatically in preimplantation mouse conceptuses just before they begin to cavitate. Moreover, localization of the enzyme in the inner membrane of the mural trophoblast is thought to be involved directly in formation and maintenance of the blastocyst cavity. Presumably,
Na
+
K
+
-
ATPase
extrudes the cation, Na
+, and therefore water into the cavity. The cation transporting activity of the enzyme can be determined by measuring ouabain-sensitive Rb
+ uptake by cells. Therefore, we measured Rb
+ uptake in mouse eggs and preimplantation conceptuses at various stages of development.
86Rb
+ uptake by conceptuses increased linearly with time for at least 60 min in medium containing 0.7 m
M total Rb
+ plus K
+ in the absence or presence of 1.0 m
M ouabain, and ouabain inhibited more than 70% of
86Rb
+ uptake. The ouabain concentration at
1
2
of maximum inhibition of the ouabain-sensitive component of
86Rb
+ uptake was about 10–20 μ
M in eggs and conceptuses at all stages of preimplantation development. Moreover, ouabain-sensitive Rb
+ uptake had a twofold higher
V
max value in blastocysts than in eggs or conceptuses at earlier stages of development (i.e., ∼173 vs 70–100 fmole · conceptus
−1 · min
−1), although the total cell surface area also was probably about two times greater in blastocysts than in eggs or other conceptuses. Ouabain-sensitive Rb
+ transport in eggs and conceptuses may have occurred via a signle ouabain-sensitive Rb
+ transporter with a Hill coefficient of 1.5–1.8 (Hill plots). When it was assumed that the Hill coefficient had a value of 2.0, however, eggs and conceptuses appeared to contain at least two forms of
Na
+
K
+
-
ATPase
activity. These studies are the first to show that the cation transporting activity of
Na
+
K
+
-
ATPase
can be measured quantitatively in mammalian eggs and preimplantation conceptuses. Inclusion of this assay in experiments designed to determine how
Na
+
K
+
-
ATPasse
activity is controlled in oocytes and conceptuses should yield further insight into the role of this enzyme in oogenesis and preimplantation development. |
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ISSN: | 0012-1606 1095-564X |
DOI: | 10.1016/0012-1606(91)90456-D |