Routes of Cl- transport across the trophectoderm of the mouse blastocyst.
The blastocyst stage of embryo development is characterized by a fluid-filled cavity called the blastocoel. Blastocoel formation requires vectorial Na+ and Cl- transport and the accompanying osmotic accumulation of fluid. We found under conditions of low external Cl- that inhibitors of Cl- transport mechanisms inhibited blastocoel expansion, indicating a possible transcellular route for Cl- uptake across the outer epithelial layer (the trophectoderm). Using the Cl--sensitive fluorophore, N-(6-methoxyquinolyl)acetoethyl ester, we found that Cl- efflux from the blastocoel can occur via pathways with properties that resemble both HCO-3/Cl- exchange and Cl- channels, as well as by another yet uncharacterized pathway. In contrast, Cl- re-uptake into Cl--depleted blastocoels (the physiologically relevant direction for Cl- transport during blastocoel expansion) occurred only via the channel-like mechanism. Patch-clamp recordings detected a component of current carried by apical Cl- channels. Intracellular pH measurements during external Cl- removal detected HCO-3/Cl- exchange activity in collapsed blastocysts but little in intact blastocysts, suggesting predominantly basolateral HCO-3/Cl- exchange activity. This was corroborated by the immunolocalization of the AE2 isoform of HCO-3/Cl- exchanger to the basolateral surface of the trophectoderm. Thus, it appears that Cl- transport into the blastocoel may occur via apical Cl- channels, while efflux also involves a basolateral HCO-3/Cl- exchanger.
Zhao
Y
Y
Ottawa Civic Hospital, University of Ottawa, Ottawa, Ontario, K1Y 4E9, Canada.
Doroshenko
P A
PA
Alper
S L
SL
Baltz
J M
JM
D000818:Animals; D017920:Antiporters / Q000502:physiology; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D001755:Blastocyst / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D004475:Ectoderm / Q000378:metabolism*; D005260:Female; D051379:Mice; D008954:Models, Biological; D011247:Pregnancy
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides