Merocyanin 540 fluorescent probe-induced changes in mechanical and electrical characteristics of lipid bilayers

Abstract

The optical probe Merocyanin 540 (M-540) has been employed _ _ to monitor action membrane potentials [l]. In using the probe it is important to know how adsorbed probe molecules modify the characteristics of the respective biological objects. The effects of M-540 on electrical characteristics of bilayer lipid membranes were studied by Krasne [2]. She reported that (1) in contrast to other voltage-sensitive dyes, M-540 induced only very small changes in BLM conductance, (2) the dye caused large changes of ionic conductivity and kinetics mediated by ionophores; these changes were considerably larger for uncharged than for charged lipids, and larger for positively charged substances than for negatively charged ones. Estimates of the transmembrane potential to explain the sudden increase of ionic conductance, based on calculations of the electrophoretic potential in compliance with the Gouy-Chapman theory, yielded too small values to explain satisfactorily the effects of M-540 on the ionic conductivity of BLM. Based on M-540 optical spectra measurements [3-51 an interaction model was developed and tested for various membrane-adsorbed dye forms. The questions arise, how these interactions affect the physical characteristics of membranes and whether they can be employed to monitor membrane characteristics. In analyzing this approach, the effects were studied of M-540 adsorption on electrical and mechanical parameters of BLMs prepared from a mixture of egg