Abstract
Charge pulse experiments [1,2] were performed in order to study the influence of local anesthetics such as procaine, benzocaine, tetracaine, lidocaine and dibucaine on ion transport through lipid bilayer membranes. The neutral lipids dioleoyllecithin (18:1 PC), dioleoylphosphatidylethanolamine (18:1 PE) as well as the negatively charged brain-phosphatidylserine (PS) were used for membrane formation. In kinetic studies with dipicrylamine (DPA−) and PV-K+ the translocation rate constants ki and kMS for the lipophilic ion and the carrier ion complex could bemeasured in the presence of the local anesthetics. It was found that the partition coefficient β of the negatively charged lipophilic ion is strongly dependent on the local anesthetics and decreases in the series procaine to dibucaine. This finding is in contrast to the hypothesis that the action of local anesthetics can be explained by an adsorption of positive charges to the membrane [3]. Our results suggest that besides an adsorption of positive charges (some local anesthetics are positively charged at pH 5–7) the dipole potential in lipid bilayer membrane (usually several hundred mV) decreases drastically by the adsorption of the local anesthetics. Its efficiency increases therefore with the increase of the hydrophobic part of the molecule.
Published Version
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