ROLE OF CHLORIDE TRANSPORT IN THE DEVELOPMENT OF THE RAT BLASTOCYST

Preimplantation mammalian development culminates in the generation of a fluid-filled cavity, the blastocoel, which requires the vectorial tr ansport of ions across the trophectoderm, followed by the movement of water. Experiments were carried out to establish the role of Cl- trans port in blastocoel formation in the rat. These included investigations of the effect of Cl- substitution and the Cl- transport inhibitors 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid, furosemide, and anth racene-9-carboxylic acid, on the development of morulae into blastocys ts in culture, and on the rate at which blastocoel fluid is accumulate d. In addition, a novel technique was developed in which the Cl--sensi tive fluorescent dye 6-methoxy-N-(3-sulfopropyl) quinolium (SPQ) was l oaded into the blastocoel cavity, in order to characterize the pathway s of transtrophectodermal Cl- transport. We established that 1) blasto coel formation in the rat requires the external presence of Cl- ions; 2) transport across the trophectoderm appears to be via a transcellula r pathway, since rates of blastocyst development, fluid accumulation, and SPQ-monitored Cl- efflux arc all reduced in the presence of Cl- tr ansport inhibitors; and 3) Cl- transport occurs via Cl-/HCO3- exchange .