Na(+)-K(+)-ATPase is distributed to microvillous and basal membrane of the syncytiotrophoblast in human placenta.
Despite its importance for placental function, syncytiotrophoblast Na(+)-K(+)-ATPase has not been studied in detail. We purified syncytiotrophoblast microvillous (MVM) and basal (BM) membranes from full-term human placenta. Western blotting with isoform-specific antibodies demonstrated the presence of the alpha(1)-subunit, but not the alpha(2)- or alpha(3)-subunits, in MVM and BM. Relative density per unit membrane protein in BM was 48 +/- 1% (mean +/- SE, n = 4, P < 0.02) of that in the MVM. The activity of Na(+)-K(+)-ATPase was lower in BM (1.4 +/- 0.14 micromol. mg(-1). min(-1), n = 8, P < 0.02) than in MVM (3.9 +/- 0.25 micromol. mg(-1). min(-1)). Immunocytochemistry confirmed the distribution of Na(+)-K(+)-ATPase to MVM and BM. These findings suggest that the syncytiotrophoblast represents a type of transporting epithelium different from the classical epithelia found in the small intestine and kidney, where Na(+)-K(+)-ATPase is confined to the basolateral membrane only. This unique polarization of the Na(+) pump does not, however, preclude a net transcellular transport of Na(+) to the fetus.
Johansson
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Perinatal Center, Department of Physiology and Pharmacology, Göteborg University, S-405 30 Göteborg, Sweden. martin.johansson@fysiologi.gu.se
Jansson
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T
Powell
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D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000201:enzymology*; D002794:Choline / Q000494:pharmacology; D004386:Duodenum / Q000166:cytology / Q000201:enzymology; D005260:Female; D006801:Humans; D007106:Immune Sera / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D017136:Ion Transport / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D008871:Microvilli / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D010920:Placenta / Q000166:cytology / Q000201:enzymology*; D011247:Pregnancy; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014327:Trophoblasts / Q000166:cytology / Q000201:enzymology*
D007106:Immune Sera; D007527:Isoenzymes; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D002794:Choline