Comparative study of the human amnion, chorion and chorioamnion permeability to monovalent cations

Amnion, chorion and chorioamnion from human term placenta were mounted between two Ussing chambers. The monovalent cation transfer was estimated by potentials (dilution, bi-ionic) and conductance measurements. This study revealed that amnion and chorioamnion discriminate the monovalent cations (the sequence is: Rb = Cs = K greater than Na greater than Li), while the chorion does not discriminate these cations. This discrimination relies on the size of the sites on the cell membrane and in intercellular spaces. The monovalent cation conductance for the three layers is gA greater than gC = gCA, and reveals that the chorioamnion properties derive in part from the properties of the isolated amnion (cationic discrimination) and those of the isolated amnion + chorion (size of sites and hydration pathways). The transfer is dependent on the three membranes' orientation and corresponds to fetal needs; the conductance ratio (g mother-fetus/g fetus-mother) is always superior to 1 when the two sides are bathed by the same medium.