Akito Takashima

Effect of dibucaine hydrochloride on raft-like lipid domains in model membrane systems

To clarify the biophysical and/or physicochemical mechanism of anaesthesia, we investigated the influence of dibucaine hydrochloride (DC·HCl), a local anaesthetic, on raft-like domains in ternary liposomes composed of dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol). The large DOPC/DPPC/Chol liposome is directly observable by optical microscopy and is known to be laterally separated into a liquid-ordered (Lo) phase (raft-like domain) and liquid-disordered (Ld) phase under certain conditions. Hence, it is useful for the study of lipid raft domains as a simple model system of cell membranes. We observed ternary liposomes with three concentrations (0, 0.05 and 0.2 mM) of DC·HCl at various temperatures and calculated the angle-averaged two-dimensional autocorrelation functions to confirm the change in miscibility transition temperature (Tc) of ternary liposomes. Furthermore, we calculated the circularity of the Lo domain to confirm the change in line tension of the Lo/Ld phase boundary. The results indicated that the insertion of DC molecules into lipid bilayers induces reduction in Tc of the ternary liposome, accompanied by reduction in line tension of the phase boundary. This suggests that the DC·HCl molecules may disturb ion channel functions by affecting the lipid bilayers surrounding the ion channels.

Confinement Effects on Polymer Dynamics: Thermo-Responsive Behaviours of Hydroxypropyl Cellulose Polymers in Phospholipid-Coated Droplets (Water-in-Oil Emulsion)

In order to construct the artificial cells and to understand the physicochemical properties of living cells, it is important to clarify the cell-sized confinement effect on the behaviours of bio-inspired polymers. We report the dynamic behaviours of aqueous hydroxypropyl cellulose (HPC) solution coated with phospholipids in oil (water-in-oil droplets, W/O droplets), accompanied by an increase in the temperature. We directly observed the beginning of phase separation of HPC solution using a fluorescence microscope and confirmed the dependence of such phenomena on droplet size. The results indicate that the start time of phase separation is decreased with an increase in droplet size. The experimental results suggest that the confinement situation accelerates the phase separation of aqueous HPC solutions.

Correction: Effect of dibucaine hydrochloride on raft-like lipid domains in model membrane systems

Correction for ‘Effect of dibucaine hydrochloride on raft-like lipid domains in model membrane systems’ by Kazunari Yoshida et al., MedChemComm, 2015, 6, 1444–1451.