I have studied the effects of four acetaldehyde-biogenic amine condensation
products on membrane fluidity of liposomes, consisting of 1-palmitoyl-2-ol
eoylphosphatidylcholine and cholesterol, by measuring fluorescence polariza
tion using different probes.
The condensation products were 1-methyl-1,2,3,4-tetrahydro-beta -carboline
(MTBC), 6-hydroxy-1 -methyl-1,2,3,4-tetrahydro-beta -carboline (6-OH-MTBC),
3-carboxy-1-methyl-1,2,3,4-tetrahydro-beta -carboline (3-C-MTBC) and 6,7-d
ihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (salsolinol). They changed
the fluidity of the hydrophobic and hydrophilic regions of liposomal membr
anes at micromolar levels almost corresponding to their antibacterial and a
ntiplatelet concentrations, but their membrane effects varied by structure,
concentration and membrane lipid composition. MTBC and salsolinol showed b
iphasic effects on the inner layers of membranes to enhance the fluidity at
250-1000 muM and reduce the fluidity at 50-100 muM, whereas both of them f
luidized the outer layers of the membranes. 3-C-MTBC concentration-dependen
tly fluidized both layers of membranes. 6-OH-MTBC most weakly enhanced and
reduced the fluidity of the outer and inner layers, respectively. The membr
ane effect of MTBC was the greatest of the four condensation products. MTBC
(50-1000 nM) significantly reduced the fluidity by exclusively acting on t
he membrane core, but was less effective in fluidizing the membrane surface
. However, the others were not active at low nanomolar levels.
The membrane effects may be partly responsible for the antibacterial and an
tiplatelet actions of the acetaldehyde-biogenic amine condensation products
, although they do not appear to be simple membrane fluidizers.