Lehtonen J Y, Kinnunen P K
Department of Medical Chemistry, University of Helsinki, Finland.
Biophys J. 1994 Jun;66(6):1981-90. doi: 10.1016/S0006-3495(94)80991-9.
Influence of osmotic shrinkage, swelling, and dehydration on large unilamellar liposomes (LUVs) of 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) was investigated using the fluorescent lipid probes 1-palmitoyl-2-[10-(pyren-1-yl)]-decanoyl-sn-glycero-3-phosphocholi ne (PPDPC) and 1,2-bis[10-(pyren-1-yl)]decanoyl-sn-glycero-3-phosphocholine (bisPDPC). Increasing concentrations of poly(ethylene glycol) (PEG, average molecular weight of 6000) producing osmotic gradients delta omega up to 250 mOsm/kg were first added to the outside of LUV labeled with 0.1 mol% of either of the above fluorescent phospholipids. The resulting osmotic shrinkage was accompanied by a progressive reduction in the lateral diffusion of the membrane-incorporated PPDPC, evident as a decrease in the rate of its intermolecular excimer formation. In contrast, under the same conditions the rate of intramolecular excimer formation by bisPDPC increased. Notably, signals opposite to those described above were observed for both of the fluorescent probes upon osmotic swelling of DOPC liposomes with encapsulated PEG. The lateral diffusion of PPDPC became progressively reduced upon membrane dehydration due to increasing concentrations of symmetrically distributed PEG (with equal polymer concentrations inside and outside of the liposomes) when neither shrinkage nor swelling occurs while enhanced excimer formation by bisPDPC was evident. The later results were interpreted in terms of osmotically induced changes in the hydration of lipids. In brief, the removal of water from the phospholipid hydration shell diminishes the effective size of the polar headgroup, which subsequently allows for an enhanced lateral packing of the phospholipid acyl chains. Our findings are readily compatible with membrane free volume Vf changes due to osmotic forces under three different kinds of stress (shrinkage, swelling, and dehydration) applied on the lipid bilayers.
使用荧光脂质探针1-棕榈酰-2-[10-(芘-1-基)]-癸酰-sn-甘油-3-磷酸胆碱（PPDPC）和1,2-双[10-(芘-1-基)]癸酰-sn-甘油-3-磷酸胆碱（bisPDPC），研究了渗透收缩、膨胀和脱水对1,2-二油酰-sn-甘油-3-磷酸胆碱（DOPC）大单层脂质体（LUVs）的影响。首先将产生高达250 mOsm/kg渗透梯度Δω的聚乙二醇（PEG，平均分子量6000）浓度增加，添加到用上述任何一种荧光磷脂的0.1 mol%标记的LUV外部。由此产生的渗透收缩伴随着膜结合PPDPC横向扩散的逐渐减少，表现为其分子间准分子形成速率的降低。相反，在相同条件下，bisPDPC的分子内准分子形成速率增加。值得注意的是，在用包封PEG的DOPC脂质体进行渗透膨胀时，上述两种荧光探针都观察到了与上述相反的信号。当脂质体内部和外部聚合物浓度相等的对称分布PEG浓度增加导致膜脱水时，PPDPC的横向扩散逐渐减少，此时既不发生收缩也不发生膨胀，而bisPDPC的准分子形成增强是明显的。后期结果根据渗透诱导的脂质水合变化进行了解释。简而言之，从磷脂水合壳中去除水会减小极性头基团的有效尺寸，这随后允许磷脂酰链的横向堆积增强。我们的发现很容易与在施加于脂质双层的三种不同应力（收缩、膨胀和脱水）下渗透力引起的膜自由体积Vf变化相符合。
