Fluid transport by rabbit preimplantation blastocysts in vitro.

Abstract

The large expansion of the rabbit blastocyst between the 3rd and 7th day post coitum(p.c.) is due to the accumulation of fluid in the blastocoele cavity (Daniel, 1964). Na+, Cl− and HCO3− appear to be actively transported across the trophectoderm into the blastocoele (Cross, 1973, 1974) and water moves passively secondary to NaCl accumulation (Borland, Biggers & Lechene, 1976; see also review by Borland, 1977). The trophoblast cell is physiologically polarized in that Na is transported into the blastocoele by Na/K pumps (Na+–K+ ATPase, E.C. 3.6.1.3) located on the juxtacoelic plasma membrane of the trophoblast cells (Biggers, Borland & Lechene, 1977). This functional polarity is also reflected by the anatomical polarity of the trophectoderm. Membrane junctional complexes are located at the apices of the trophoblast cell and are adjacent to fluid-filled intercellular spaces that face the blastocoele cavity (Gamow & Daniel, 1970; Enders, 1971; Hastings & Enders, 1975; Ducibella, Albertini, Anderson & Biggers, 1975). Diamond & Bossert (1967) have proposed that such closed-end channels may be the site of active solute transport that creates local standing osmotic gradients which cause water flow across epithelia.