Effects of Cholesterol—Sphingomyelin Interactions on Penetration of Neuropeptides to their Monolayers

Abstract

ABSTRACTIn the present study, the surface behavior and interactions between the synthetic analogue of the endogenous neuropeptide Methionine-enkephalin (Met-enk) and monolayers composed of cholesterol (Chol), sphingomyelin (SM) and their mixtures are studied. The measurements are made by using Langmuir's monolayer technique simultaneously with Wilhelmy method for determination of monolayer (on subphase of 0,14 M NaCl) surface tension as a function of time and lipid molecular area. After the injection of the Met-enk into the subphase, a decrease in surface tension is detected in all experiments. The data obtained show that the peptide penetrates the monolayers of both lipid types as well as of their mixtures. It is proved that, regarding the Met-enk penetration, there is a synergetic effect in the mixed monolayers of Chol and SM. Most probably, this is due to the ability of cholesterol to regulate the fluidity of lipid monolayers. Thus, we suggest that Chol facilitates the penetration of the neuropeptide in SM monolayer films.