Wehrli S, Ramirez C, Kraus J L, Castaing M
Centre de Biochimie et de Biologie Moléculaire, CBM2/CNRS, Marseille, France.
Biochim Biophys Acta. 1992 Jun 30;1107(2):319-30. doi: 10.1016/0005-2736(92)90419-m.
Temperature-jump relaxation experiments on Na+ transport by (221)C10-cryptand were carried out in order to study the influence of cholesterol and its temperature-dependence on ion transport through thin lipid membranes. The experiments were performed on large, negatively charged unilamellar vesicles (LUV) prepared from mixtures of dioleoylphosphatidylcholine, phosphatidic acid and cholesterol (mole fractions 0-0.43), at various temperatures and carrier concentrations. The initial rates of Na+ transport and the apparent rate constants of its translocation by (221)C10 increased with the carrier concentration and the temperature. The incorporation of cholesterol into the membranes significantly reduced the carrier concentration- and temperature-dependence of these two parameters. The apparent energy required to activate the transport decreased significantly with increasing carrier concentrations at any given cholesterol molar fraction, and increased significantly with the cholesterol molar fraction at any given carrier concentration. Our interpretation of the action of cholesterol on this transport system is based on the assumption that the binding cavity of cryptands is likely to be located towards the aqueous side of the dipole layer. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes, and of the interactions occurring between an ionizable mobile carrier and the membrane.
为了研究胆固醇及其温度依赖性对离子通过薄脂质膜运输的影响，我们对（221）C10-穴醚介导的Na+运输进行了温度跃变弛豫实验。实验是在由二油酰磷脂酰胆碱、磷脂酸和胆固醇（摩尔分数0 - 0.43）的混合物制备的大的带负电荷的单层囊泡（LUV）上进行的，实验在不同温度和载体浓度下进行。Na+运输的初始速率及其通过（221）C10转运的表观速率常数随载体浓度和温度的升高而增加。将胆固醇掺入膜中显著降低了这两个参数对载体浓度和温度的依赖性。在任何给定的胆固醇摩尔分数下，激活运输所需的表观能量随载体浓度的增加而显著降低，并且在任何给定的载体浓度下，随胆固醇摩尔分数的增加而显著增加。我们对胆固醇在该运输系统中作用的解释基于这样的假设，即穴醚的结合腔可能位于偶极层的水相一侧。我们从载体和复合物的结构、物理化学和电学特性，以及可电离的移动载体与膜之间发生的相互作用方面讨论了这些结果。
