Local anesthetic-phospholipid interactions. The pH dependence of the binding of dibucaine to dimyristoylphosphatidylcholine vesicles.

The interaction of the local anesthetic dibucaine with unilamellar vesicles of dimyristoylphosphatidylcholine was studied by equilibrium dialysis. Saturating binding profiles (as a function of dibucaine) were found, with apparent association constant ranging from 1.26 X 10(3)M-1 to 2.57 X 10(3)M-1 as pH is increased from 5.0 to 7.5. The number of phospholipid molecules comprising a binding site was found to be about 5 at each pH. Analysis of the data was also achieved using the Stern model, which takes into account the electrostatic effect on binding of the cationic drug due to the build up of a surface potential.