Kinjo M, Araiso T, Koyama T
Research Institute of Applied Electricity, Hokkaido University, Sapporo, Japan.
Biorheology. 1988;25(3):517-25. doi: 10.3233/bir-1988-25311.
Membrane fluidity and osmotic sensitivity were examined in DPPC liposomes treated with phospholipase A2 (PL.A2) in the presence of Ca2+ or Mg2+. The amount of liposome phospholipid hydrolyzed differed with the two ions. Embedded DPH, a rod-like fluorescent probe, was employed in the determination of membrane fluidity. Membrane fluidity decreased according to the degree of phospholipid hydrolization in liposomes by PL.A2. The reciprocal value of absorption at 450 nm was measured as the index of osmotic sensitivity of liposomes. Intact sonicated liposomes showed osmotic insensitivity. PL.A2-treated liposomes in which about 40% of total phospholipid was hydrolyzed showed osmotic sensitivity. No change in the membrane fluidity was obtained when PL.A2-treated liposomes were exposed to hypertonic or hypotonic solution. These results suggested that the motion of the acyl-chain of phospholipids and free fatty acids was resisted in PL.A2-treated liposomes. The resistance may be due to a phase separation between phospholipids and free fatty acids. The pore for water permeation might be induced in the border between phase-separated domains in PL.A2-treated liposomes.
在 Ca2+ 或 Mg2+ 存在的情况下，对用磷脂酶 A2（PL.A2）处理的二棕榈酰磷脂酰胆碱（DPPC）脂质体的膜流动性和渗透敏感性进行了检测。脂质体磷脂的水解量因这两种离子而有所不同。使用嵌入的棒状荧光探针二苯基己三烯（DPH）来测定膜流动性。膜流动性根据 PL.A2 对脂质体中磷脂的水解程度而降低。测量 450 nm 处吸收的倒数作为脂质体渗透敏感性的指标。完整的超声处理脂质体表现出渗透不敏感性。约 40% 的总磷脂被水解的 PL.A2 处理脂质体表现出渗透敏感性。当 PL.A2 处理的脂质体暴露于高渗或低渗溶液时，膜流动性没有变化。这些结果表明，在 PL.A2 处理的脂质体中，磷脂的酰基链和游离脂肪酸的运动受到了阻碍。这种阻碍可能是由于磷脂和游离脂肪酸之间的相分离。在 PL.A2 处理的脂质体中，相分离区域之间的边界可能诱导了水渗透的孔隙。
