Alvarez P E, Gervasi C A, Vallejo A E
Instituto de Física, Facultad de Bioquímica, Química y Farmacia, UNT, Tucumán, Argentina.
J Biol Phys. 2007 Dec;33(5-6):421-31. doi: 10.1007/s10867-008-9072-5. Epub 2008 May 13.
Kinetics of facilitated ion transport through planar bilayer membranes are normally analyzed by electrical conductance methods. The additional use of electrical relaxation techniques, such as voltage jump, is necessary to evaluate individual rate constants. Although electrochemical impedance spectroscopy is recognized as the most powerful of the available electric relaxation techniques, it has rarely been used in connection with these kinetic studies. According to the new approach presented in this work, three steps were followed. First, a kinetic model was proposed that has the distinct quality of being general, i.e., it properly describes both carrier and channel mechanisms of ion transport. Second, the state equations for steady-state and for impedance experiments were derived, exhibiting the input-output representation pertaining to the model's structure. With the application of a method based on the similarity transformation approach, it was possible to check that the proposed mechanism is distinguishable, i.e., no other model with a different structure exhibits the same input-output behavior for any input as the original. Additionally, the method allowed us to check whether the proposed model is globally identifiable (i.e., whether there is a single set of fit parameters for the model) when analyzed in terms of its impedance response. Thus, our model does not represent a theoretical interpretation of the experimental impedance but rather constitutes the prerequisite to select this type of experiment in order to obtain optimal kinetic identification of the system. Finally, impedance measurements were performed and the results were fitted to the proposed theoretical model in order to obtain the kinetic parameters of the system. The successful application of this approach is exemplified with results obtained for valinomycin-K(+) in lipid bilayers supported onto gold substrates, i.e., an arrangement capable of emulating biological membranes.
促进离子通过平面双层膜传输的动力学通常用电导方法进行分析。为了评估各个速率常数，还需要额外使用电弛豫技术，如电压阶跃。尽管电化学阻抗谱被认为是现有电弛豫技术中最强大的，但它很少与这些动力学研究结合使用。根据本文提出的新方法，遵循了三个步骤。首先，提出了一个具有通用性的动力学模型，即它能恰当地描述离子传输的载体和通道机制。其次，推导了稳态和阻抗实验的状态方程，展示了与模型结构相关的输入-输出表示。通过应用基于相似变换方法的一种方法，可以检验所提出的机制是可区分的，即没有其他具有不同结构的模型对于任何输入都表现出与原始模型相同的输入-输出行为。此外，该方法使我们能够检验在所提出的模型根据其阻抗响应进行分析时是否全局可识别（即该模型是否存在一组唯一的拟合参数）。因此，我们的模型并非对实验阻抗的理论解释，而是构成了选择此类实验以获得系统最佳动力学识别的前提条件。最后，进行了阻抗测量，并将结果拟合到所提出的理论模型中以获得系统的动力学参数。这种方法的成功应用通过在支撑于金基底上的脂质双层中缬氨霉素 - K⁺ 的实验结果得到了例证，即一种能够模拟生物膜的装置。
