Ouabain-sensitive fluid accumulation and ion transport by rabbit blastocysts

1. By incubating 6-day post-coitum (p.c.) blastocysts in medium supplemented with either 20 mM-sucrose or 10 mM-KCl it was possible to show that the trophectoderm of the blastocyst prevents the concentration of K in the blastocoele fluid rising to external concentrations. 2. The concentrations of K in the blastocoele fluid are maintained predominantly by leakage of K from the trophoblast cells into the blastocoele and by ouabain-sensitive transport of K into the trophoblast cells from the blastocoele fluid. 3. Exposure of blastocysts to ouabain on the juxtacoelic, but not abcoelic, surface of the trophectoderm may inhibit blastocoele fluid accumulation.