Vareille G, Marion P, Kraus J L, Castaing M
Centre de biochimie et de biologie moléculaire, CBM2/CNRS 31, Marseilles, France.
Biochim Biophys Acta. 1993 Feb 23;1146(1):25-37. doi: 10.1016/0005-2736(93)90334-v.
Temperature-jump relaxation experiments on Na+ transport by (221)C10-cryptand (ionizable mobile carrier) and nonactin (neutral mobile carrier) were carried out in order to study the effects of cholesterol and the degree of acyl chain unsaturation, and their temperature-dependence on ion transport through thin lipid membranes. The experiments were performed on large, negatively charged unilamellar vesicles (LUV) prepared from mixtures of phosphatidylcholine (egg phosphatidylcholine, dioleoylphosphatidylcholine and dilinoleolylphosphatidylcholine), phosphatidic acid and cholesterol (mole fractions 0-0.43), at various temperatures and carrier concentrations. The apparent rate constants of Na+ translocation by (221)C10 and nonactin increased with the carrier concentration, the degree of acyl chain unsaturation and the temperature. The incorporation of cholesterol into the membranes significantly reduced the carrier concentration-, acyl chain unsaturation- and temperature-dependence of this parameter. The apparent energy required to activate the transport decreased significantly with increasing (221)C10 concentrations and remained constant with increasing those of nonactin at any given cholesterol molar fraction and degree of acyl chain unsaturation. It increased significantly with increasing the cholesterol molar fraction at any given carrier concentration to an extent depending on the degree of acyl chain unsaturation. Our interpretation of the action of cholesterol on these transport systems is based on the assumption that the adsorption plane of Na(+)-(221)C10 and Na(+)-nonactin complexes is likely to be located towards the aqueous and the hydrocarbon side of the dipole layer, respectively. 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 or a neutral mobile carrier and the membrane.
为了研究胆固醇和酰基链不饱和度的影响及其对通过薄脂质膜的离子转运的温度依赖性，对由（221）C10 - 穴状配体（可电离移动载体）和缬氨霉素（中性移动载体）介导的Na⁺转运进行了温度跃变弛豫实验。实验是在由磷脂酰胆碱（卵磷脂、二油酰磷脂酰胆碱和二亚油酰磷脂酰胆碱）、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。由（221）C10和缬氨霉素介导的Na⁺转运的表观速率常数随载体浓度、酰基链不饱和度和温度的增加而增加。向膜中掺入胆固醇显著降低了该参数对载体浓度、酰基链不饱和度和温度的依赖性。在任何给定的胆固醇摩尔分数和酰基链不饱和度下，激活转运所需的表观能量随（221）C10浓度的增加而显著降低，随缬氨霉素浓度的增加保持恒定。在任何给定的载体浓度下，它随胆固醇摩尔分数的增加而显著增加，增加程度取决于酰基链不饱和度。我们对胆固醇在这些转运系统中作用的解释基于这样的假设，即Na⁺ - （22）C10和Na⁺ - 缬氨霉素复合物的吸附平面可能分别位于偶极层的水相和烃相一侧。根据载体和复合物的结构、物理化学和电学特性，以及可电离或中性移动载体与膜之间发生的相互作用对结果进行了讨论。
