La3+ and Gd3+ induce shape change of giant unilamellar vesicles of phosphatidylcholine

Abstract Lanthanides such as La 3+ and Gd 3+ are well known to have large effects on the function of membrane proteins such as mechanosensitive ionic channels and voltage-gated sodium channels, and also on the structure of phospholipid membranes. In this report, we have investigated effects of La 3+ and Gd 3+ on the shape of giant unilamellar vesicle (GUV) of dioleoylphosphatidylcholine (DOPC-GUV) and GUV of DOPC/cholesterol by the phase-contrast microscopy. The addition of 10–100 μM La 3+ (or Gd 3+ ) through a 10-μm diameter micropipette near the DOPC-GUV (or DOPC/cholesterol-GUV) triggered several kinds of shape changes. We have found that a very low concentration (10 μM) of La 3+ (or Gd 3+ ) induced a shape change of GUV such as the discocyte via stomatocyte to inside budded shape transformation, the two-spheres connected by a neck to prolate transformation, and the pearl on a string to cylinder (or tube) transformation. To understand the effect of these lanthanides on the shape of the GUV, we have also investigated phase transitions of 30 μM dipalmitoylphosphatidylcholine-multilamellar vesicle (DPPC-MLV) by the ultra-sensitive differential scanning calorimetry (DSC). The chain-melting phase transition temperature and the L β′ to P β′ phase transition temperature of DPPC-MLV increased with an increase in La 3+ concentration. This result indicates that the lateral compression pressure of the membrane increases with an increase in La 3+ concentration. Thereby, the interaction of La 3+ (or Gd 3+ ) on the external monolayer membrane of the GUV induces a decrease in its area ( A ex ), whereas the area of the internal monolayer membrane ( A in ) keeps constant. Therefore, the shape changes of the GUV induced by these lanthanides can be explained reasonably by the decrease in the area difference between two monolayers (Δ A = A ex − A in ).