Response of the electrochromic dye, merocyanine 540, to membrane potential in rat liver mitochondria

Abstract

Merocyanine binds extensively to rat liver mitochondria in spite of the presence of a sulfonic acid group which would suggest only limited penetration through the membrane. Passive binding shows both tight and weak binding components and is dependent on salt concentration and ionic strength in accord with the Gouy-Chapman theory. The binding of merocyanine to mitochondria is accompanied by both a fluorescence enhancement and a spectral shift. Induction of an electrical field by either respiration or K+ diffusion potential results in a partial reversal of the spectral shift seen on dye binding. At low temperature, the merocyanine spectral response to an electrical field is biphasic, consisting of a fast phase with a t1/2 of less than 1 sec at 15 degrees C and a slower phase which may vary considerably in rate and extent with conditions. The spectral shift during the two phases appears similar, but differ in sensitivity to ionic strength and temperature. The spectral shift during the fast phase at 15 degrees C indicates that the major component is a decrease in bound monomer and an increase in the aqueous dimer, indicating an "on-off" mechanism. It is suggested that the fast and slow phases of the merocyanine response may be due to two different populations of dye, possibly located at the outer and inner surfaces, respectively, of the mitochondrial membrane. The electrophoretic movement of the dye located in the membrane interior would result in the temperature-sensitive slow phase response. Demonstration of the proportionality of the fast phase response to the magnitude of the membrane potential suggests the usefulness of merocyanine in studies with mitochondrial systems.

Quantification of lipid bilayer effective microviscosity and fluidity effect induced by propofol

“…Using this correlation, we Some anaesthetics have been shown to alter the membrane fluidity and depress the phase transition temperature [12]. The fluidity alterations have been previously described qualitatively by measuring a decrease in the order parameter [28]. Adding PPF (% 20 mM) in DMPC at 25°C, i.e.…”

The components of merocyanine‐540 absorption spectra in aqueous, micellar and bilayer environments

“…This is in contrast to most MC540-membrane studies where the cyanine is added to formed liposomes, in order to elucidate the dye-binding conditions in the light of its selective cell staining and potentiometric properties. In so doing the spectra will feature only the outer monolyer, because MC540 membrane translocation will be very limited due to its SO; group [6,191.…”

“…The major factor influencing dimer formation is not the density of the phospholipid-head groups, but the packing of the adjacent hydrocarbon region. Substances which exhibit a condensing action at this level are cholesterol, gramicidin A and probably the dye itself, for the dimer proportion increases when the MC540-membrane concentration is enhanced [6].…”

Effect of Membrane Potential on the Binding of Merocyanine 540 to Human Erythrocytes

“…BSA, bovine serum albumin; DiS-C3-(5), 3.3'-dipropylthiadicarbocyanine iodide; EGTA, ethyleneglycol-bis-(P-aminoethyl ether) N,N'-tetraacetic acid; MC540, merocyanine 540; PBS, phosphatebuffered saline; Tris, tris(hydroxymethy1)aminomethane; A'P, membrane potential. 0 1998 American Society for Photobiology 0031-8655198 $5.00+0.00 mid-seventies MC540 was frequently used as a probe to monitor transmembrane potential changes in nerve cells, mitochondria and liposomes (3)(4)(5)(6)(7). However, because of its phototoxicity, MC540 has been largely replaced by other dyes, like the carbocyanides.…”