Comparative effects of MgCl2 and MgSO4 on the ionic transfer components through the isolated human amniotic membrane.

The effects of MgCl2 and MgSO4 are different on the total transfer through the human amniotic membrane: MgCl2 at low concentration (1 mM) decreases the total conductance Gt and increases it at high concentration (4 mM) on the fetal side (FS) and on the maternal side (MS), while MgSO4 has no effect on the MS and increases Gt on the FS. Moreover, whatever the concentration, MgCl2 increases the flux ration F1/F2 while MgSO4 decreases it to reach a value near to 1. Gt is the sum of various components: three paracellular components (Gp) and nine cellular components (Gc constituted from channels, exchangers, antiporters and cotransporters). All components of Gt, on the two faces, are decreased by 1 mM MgCl2 and increased at 4 mM. MgCl2 also has an effect on all ionic exchangers across the membrane. In contrast, on the MS, MgSO4 (1 mM) decreases GpNa, increases GpK and the antiport Na/H component and has no effect on any of the other components, while at 4 mM, MgSO4 has no effect. On the FS, MgSO4 (1 mM) increases GpNa and GpK, but does not modify the other components. At 4 mM, the effect is the same, except for an increase of GpCl. These data show the importance of the anion-cation association in the ionic exchanges through a membrane: MgCl2 and MgSO4 have a different action--MgCl2 interacts with all the exchangers, while the effect of MgSO4 is limited to paracellular components without interaction with cellular components excepted the antiport Na/H.