BINDING OF LOCAL-ANESTHETIC TETRACAINE TO PHOSPHOLIPID MIXED VESICLES

We measured the binding isotherms of a local anesthetic, tetracaine, to dilauroylphosphatidic acid (DLPA) and dilauroylphosphatidylcholine (DLPC) mixed vesicles along with their pure vesicles. The binding isotherms were constructed by the equilibrium dialysis method at different pH (5.5, 7.0, 8.0) at 35-degrees-C. The binding isotherms were analyzed based on the equations combined with Langmuir and Hill-type isotherms, and the parameters characterizing the binding isotherms were evaluated. The thus-obtained binding parameters for pure vesicles well reproduce the binding isotherms for the mixed vesicles by taking account of the mixing ratios. This indicates that DLPA and DLPC also provide independent binding sites for tetracaine, as for previously reported dibucaine. The estimated values of the binding parameters for these two anesthetics, i.e., tetracaine and dibucaine, were compared in terms of the strength of the anesthetic action as well as the molecular structure.