Fluorescence and thermodynamics studies of the interaction of the local anesthetic dibucaine with model membranes

摘要

The interaction of dibucaine with model membrane systems has been studied using both equilibrium dialysis and time-resolved fluorescence methods. Binding isotherms, for the interaction of dibucaine with unilamellar phospholipid vesicles, were obtained as a function of ionic strength and as a function of initial surface charge on the vesicles. The binding of dibucaine is shown to be significantly influenced by electrostatic interactions; binding isotherms were fitted with a Guoy-Chapman-Stern model in terms of an intrinsic dissociation constant of 2.9 mM and a maximum extent of binding of approximately one drug molecule per phospholipid molecule. Various state steady-state and time- resolved fluorescence studies were performed to characterize the topography and dynamics of dibucaine molecules which are bound to the phospholipid vesicles. Quenching studies with KI show bound dibucaine to be protected from the anionic quencher. The fluorescence lifetime of free and vesicles-bound dibucaine is found to be 3.3 and approximately 2.6 ns, respectively. Anisotropy decay measurements indicate that the effective rotational correlation time of bound dibucaine is increased to approximately 4 ns, as compared to a value of 0.06 ns for free dibucaine. An infinitely long rotational correlation time (or a r$-$INF$/) was not observed for bound dibucaine, indicating that the rotational motion of bound dibucaine is isotropic.