Developmental changes in epithelial transport characteristics of preimplantation rabbit blastocysts.

Abstract

Transepithelial sucrose and urea permeability coefficients were measured in different-aged preimplantation rabbit blastocysts. Sucrose permeability remained constant from 4-6 days after fertilization (.apprx. 1 .times. 10-8 cm s-1), but thereafter increased. Urea permeability was very low throughout this period (5 .times. 10-7 cm s-1) but a phloretin-sensitive component to urea influx appeared between days 6/7 post coitum (p.c.). Glucose uptake was small (0.2-0.5 nmol cm-2 s-1) and independent of external sodium throughout the preimplantation period. Methionine uptake was 10 times greater than glucose uptake, and was strongly dependent upon the presence of external Na in 5 and 6 day p.c. blastocysts. The Na dependence of methionine uptake was lost by the 7th day after fertilization. The transepithelial electrical resistance was always < 35 .omega. cm2 in 4 day p.c. blastocysts, and averaged 1758 .omega. cm2 in 6 day p.c. blastocysts. The transepithelial influx of 140La averaged 0.46 .+-. 0.11 nmol cm-2 h-1 (n = 6) in 4 day p.c. blastocysts. The 5 day p.c. embryos were impermeable to La (n = 10). The epithelium of the preimplantation rabbit blastocyst apparently undergoes dramatic changes in transport characteristics with development. The blastocyst can be characterized as a leaky transporting epithelium during the early blastocyst period, and as a tight epithelium during the mid to late stages of the preimplantation period.