A new method of in vitro prescreening evaluation of the relationship between toxic and common metal ions.

The human amniotic membrane, an asymmetrical and nonexcitable epithelium with sites differently situated on the fetal and maternal sides, may be considered a model for investigating the relationship between toxic and common metal ions. The method is based on the observation of the ionic transfer across the amnion, estimated by measuring the total ionic conductance Gt from the mother to the fetus and from the fetus to the mother. It is important to note that opposite effects between two ions are not necessarily correlated with antagonism; indeed, pollutants decrease ionic conductance Gt and Mg increases it, but Mg is not an antagonist of all pollutants. To define antagonism between two ions, the Dixon curves theory should be applied. These curves represent the variation of Gt when the concentration of common metal increases (1 mM, 3 mM), while the concentration of toxic metal is maintained constant (3 concentrations of toxic metal are used). The straight lines obtained are either parallel to each other (noncompetitive inhibition), parallel to the x axis (no interaction between common and toxic metals), or the 3 lines intersect at a common point equal to the inhibition constant. At pharmacological doses, there is competitive inhibition (specific antagonism) between Mg and Cd, Zn and Cd, Ca and Cd, and Mg and Pb, and noncompetitive inhibition between Mg and Hg. This method may rapidly indicate a membrane interaction between common and toxic metals.