Ciani S, Gambale F, Gliozzi A, Rolandi R
J Membr Biol. 1975 Oct 16;24(1):1-34. doi: 10.1007/BF01868613.
Some effects of diffusion polarization and chemical reactions on the steady-state zero-current conductance of lipid bilayers mediated by neutral carriers of ions have been studied theoretically and experimentally. Assuming that ion permeation across the interfaces occurs via a heterogeneous reaction between ions in the solution and carriers in the membrane, the relationship between the conductance and the aqueous concentration of carriers is shown to be linear only in a limited range of sufficiently low concentrations. At higher carrier concentrations, which for the most strongly bound cations are within the range of the experimentally accessible values, the conductance is expected to become limited by diffusion of the carried ion in the unstirred layers and therefore reach an upper limiting value independent of the membrane properties. This expectation has been successfully verified for glyceryl-monooleate membranes in the presence of the ions K+, Rb+ and NH+4 and carriers such as valinomycin and trinactin. The experimental results support, at least for the present system, the generally accepted view that complexation between ions and the macrocyclic antibiotics occurs at the membrane surface; it is shown, in fact, that for a different mechanism, such as that by which the complexes would form in the aqueous solutions and cross the interfaces as lipid-soluble ions, the same type of saturation would be expected to be observable only for unrealistically high values of the rate constants of the ion-carrier association. A previously proposed criterion to distinguish between these two mechanisms, based on the dependence of the conductance on the ion concentration, is discussed from the viewpoint of this more comprehensive model.
理论和实验研究了扩散极化和化学反应对由离子中性载体介导的脂质双层稳态零电流电导的一些影响。假设离子跨界面渗透是通过溶液中的离子与膜中的载体之间的异质反应发生的，结果表明，仅在足够低浓度的有限范围内，电导与载体的水相浓度之间的关系才是线性的。对于结合最强的阳离子，在实验可及的浓度范围内，较高的载体浓度下，电导预计将受到被携带离子在未搅拌层中扩散的限制，因此达到一个与膜性质无关的上限值。对于存在K +、Rb +和NH + 4离子以及缬氨霉素和三联抗生素等载体的甘油单油酸酯膜，这一预期已得到成功验证。实验结果至少对于当前系统支持了普遍接受的观点，即离子与大环抗生素之间的络合发生在膜表面；事实上，结果表明，对于不同的机制，例如络合物在水溶液中形成并作为脂溶性离子穿过界面的机制，预计只有在离子 - 载体缔合速率常数的不切实际的高值下才能观察到相同类型的饱和现象。从这个更全面的模型的角度讨论了先前提出的基于电导对离子浓度的依赖性来区分这两种机制的标准。
