  We investigated the effect of Dibucaine hydrochloride (DC$\cdot$HCl), one of
the local anesthetics, on phase behavior of ternary liposome composed of
dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC), and
cholesterol (Chol). The large DOPC/DPPC/Chol liposome, that is directly
observable by optical microscope, is commonly known to be laterally separated
into liquid-ordered (Lo) phase (raft-like domain) and liquid-disordered (Ld)
phase under certain conditions and is useful for study of lipid-raft-like
domains as a simple model system. In order to confirm the effect of
DC$\cdot$HCl on a miscibility transition temperature, $T_{\rm c}$, of the
ternary liposome, we observed the liposomes with three concentrations, 0, 0.05,
and 0.2~mM, of DC$\cdot$HCl at various temperatures. In addition, we calculated
the angle-averaged two-dimensional autocorrelation (2D-AC) functions in order
to quantify the phase behavior. The results of these observations and
calculations revealed that the DC$\cdot$HCl molecules induce the reduction of
$T_{\rm c}$ of the ternary liposome. Furthermore, we calculated the circularity
of Lo domain in order to confirm the change in the line tension of the Lo/Ld
phase boundary and revealed that the insertion of the DC molecules induces the
reduction of line tension. In terms of the critical phenomena, we conclude that
the insertion of the DC molecules induces the reduction of the $T_{\rm c}$ of
the ternary liposome due to reduction of line tension. This suggests that the
DC molecules may disturb function of ion channels via affecting the lipid
bilayers which surround ion channels.
