La~(3+) and Gd~(3+0 induce shape change of giant unilamellar vesicles of phosphatidylcholine

摘要

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 (10μM) 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 (△A=A~(ex)-A~(in)).