Cationic atmosphere and cation competition binding at negatively charged membranes: pathological implications of aluminum.

Binding of cations to membranes may be the basis for explaining some of the effects of several neurotoxic cations. The binding of Al3+ and the displacement of Ca2+ by Al3+ is studied with the aid of a simple mathematical approach described here and giving the same results when compared to the mathematical formalism described by Nir and Bentz. The method allows the simulation of membranes with low surface charge densities that are relevant for biochemical and pathological implications. Fluorescence quenching of the phospholipid analogue 1-palmitoyl-2-nitrobenzoxadiazol amino caproyl- phosphatidyl choline (C6-NBD-Ptd Cho) embedded in phosphatidyl serine membranes is used to determine the competition between calcium and aluminum for binding. The effect of aluminum in the presence of chelating agents is also studied by quenching experiments. Finally, inhibition of 45Ca2+ binding to phosphatidyl serine has also been investigated in a two-phase system.