Accatino L, Gavilan P
Department of Gastroenterology, School of Medicine, Pontificia Universidad Catolica de Chile, Santiago.
Hepatology. 1988 Jul-Aug;8(4):898-903. doi: 10.1002/hep.1840080432.
Phospholipids and bile acids, by virtue of their amphiphilic properties, can interact in nonpolar media forming "inverted" structures (micelles) which presumably have an hydrophilic core and might act as diffusional carriers (ionophores) of electrolytes across low dielectric constant media or lipid membranes. The Na+ ionophoretic capability of various purified phospholipids and the modulating effects of bile acids and phosphatidylcholine was examined by: (a) measurement of 22Na+ partition into the organic phase (chloroform) of a two-phase system and (b) direct measurement of the translocation of 22Na+ across a bulk chloroform phase separating two aqueous phases in a Pressman cell. All phospholipids tested, except for phosphatidylcholine, showed ionophoretic capability for Na+ at micromolar concentrations. Cardiolipin and phosphatidylserine were the most efficient Na+ carriers, comparable with monensin, an established Na+ ionophore. In contrast, cholic acid as well as other bile acids demonstrated only marginal or no Na+ ionophoretic capability. However, hydroxylated bile acids (particularly cholic acid), sodium dodecyl sulfate and Triton X-100, which can induce and stabilize inverted structures in lipid membranes, were able to increase 5- to 8-fold the phospholipid-mediated Na+ transport. Interaction of cardiolipin with Na+ in the chloroform phase followed a rectangular hyperbolic function with an apparent Kd within the physiological Na+ concentration range (16.9 +/- 5.1 mM). Addition of cholic acid to the cardiolipin-containing organic phase resulted in a 10-fold increase of maximal Na+ uptake and no change in apparent Kd. The effect of cholic acid on both cardiolipin-mediated Na+ partition and Na+ translocation across the chloroform phase showed a marked dependence on pH, being greater at pH 7.4.(ABSTRACT TRUNCATED AT 250 WORDS)
磷脂和胆汁酸因其两亲性，可在非极性介质中相互作用形成“倒置”结构（胶束），这种结构可能具有亲水性核心，并可能作为电解质穿过低介电常数介质或脂质膜的扩散载体（离子载体）。通过以下方法研究了各种纯化磷脂的Na⁺离子载体能力以及胆汁酸和磷脂酰胆碱的调节作用：（a）测量²²Na⁺在两相系统的有机相（氯仿）中的分配，以及（b）直接测量²²Na⁺在Pressman池中穿过分隔两个水相的大量氯仿相的转运。除磷脂酰胆碱外，所有测试的磷脂在微摩尔浓度下均显示出对Na⁺的离子载体能力。心磷脂和磷脂酰丝氨酸是最有效的Na⁺载体，与已确定的Na⁺离子载体莫能菌素相当。相比之下，胆酸以及其他胆汁酸仅表现出微弱的或没有Na⁺离子载体能力。然而，可诱导并稳定脂质膜中倒置结构的羟基化胆汁酸（特别是胆酸）、十二烷基硫酸钠和 Triton X-100，能够使磷脂介导的Na⁺转运增加5至8倍。心磷脂与氯仿相中的Na⁺相互作用遵循矩形双曲线函数，在生理Na⁺浓度范围（16.9±5.1 mM）内具有表观解离常数（Kd）。向含有心磷脂的有机相中添加胆酸导致最大Na⁺摄取增加10倍，而表观Kd没有变化。胆酸对心磷脂介导的Na⁺分配和Na⁺穿过氯仿相的转运的影响显示出对pH的显著依赖性，在pH 7.4时更大。（摘要截断于250字）
