Active Sodium and Chloride Transport Across The Rabbit Blastocoele Wall

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Abstract
Ion transport processes of the 6-day rabbit blastocyst were examined in vitro by measuring unidirectional fluxes of 22Na and 36Cl across the short-circuited preparation. When Eagle’s medium (20% calf serum) containing 25 mM HCO3 bathed both sides of the blastocoele and the transmural potential difference was reduced to zero, there was a net Na flux (0.58 ± 0.15 μM/cm2/h) and a net Cl flux (0.59 ± 0.14 μM/cm2/h) from the outside bathing solution to the blastocoele. Net Na and Cl fluxes were both three times larger than the short-circuit current and accounted for only 5% of the short-circuit current. Changing the outside bathing medium to a HCO3-free solution greatly reduced the potential difference and short-circuit current, whereas removal of Na and Cl ions from the outside solution had no effect. It is concluded that Na and Cl are actively transported into the rabbit blastocoele, and the presence of an appropriately directed unidentified component of short-circuit current, which is greatly reduced in HCO3-free solutions, suggests that the rabbit blastocyst also actively transports HCO3.

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