Ca2 binding and translocating properties of diflunisal

We have characterized the binding of Ca2+ and Mg2+ to the anti-inflammatory drug diflunisal in acetonitrile and demonstrated the drug-mediated transport of Ca2+ across the lipid bilayer in unilamellar vesicles made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. Fluorescence and difference absorption spectral data show that diflunisal undergoes a significant conformational change on binding Ca2+ and Mg2+ forming, respectively, 1:2 and 1:1 cation:drug complexes with Kd in the low microM range. The kinetics of transport showed that Ca2+ was transported into the vesicle as 1:2 Ca2+:diflunisal sandwich complex. This suggests that the interaction of the drug with the cation in the lipid-mimetic solvent are similar. The biological relevance of the Ca(2+)-binding and translocating abilities of diflunisal is examined in light of the reported ionophoretic properties of several phospholipids as well as cyclooxygenase and lipoxygenase products.