Monnier A M
Rev Can Biol Exp. 1982 Mar;41(1):47-63.
Solubility of narcotics in lipids has promoted the quest for non-aqueous and lipidic models of cell membranes. Artificial phosphatidic bilayers have been proposed. They display ionic conductance and excitability only if they are in contact with cyclic ion-carrier or specific substances, such as the protein fraction EIM. However many lipidic substances form non-bilayer membranes ion-conducting and excitable, without any specific additive. Only a small amount of free fatty acid is necessary. This is the condition for penetration through cation exchange. Coloured cations and cationic drugs undergo large exchange. Cu++, Hg++, emetine ++ cations have very high exchange coefficients which can be experimentally measured and which explain their respective antifungal, antibacterial and antiamoebian actions. The possible processes of membrane excitation are discussed. First the classical pores, specific of K+ and Na+ transfers and their "gating" mechanisms, because cell membranes are bi-ionic systems. Artificial membranes, are mono-ionic systems. But recent work shows that the axon membrane can be transformed into a monoionic system with Co++ as the only cations inside and outside the axon. Suggestions for the excitation processes are proposed. a) The assumption of a single energy barrier corresponding to minor conformational changes of structure. b) The membrane may be thixotropic. An outside cation penetrating the membrane would leave behind itself a wake of fluidity into which the next cations could penetrate if they follow each other closely. If they progress widely apart (under a small field), the ionic current would soon stop as the structure solidifies. c) The most promising suggestion is that anionic fixed charges in the membranes and cations form electrostatically bound ion-pairs. Dissociation of such pairs, that is conductance, augments markedly when dielectric constant increases. This process could be produced by water carried by incoming cations, that is by electro osmosis. This is exactly what occurs in Teorell's membrane oscillator in which a model membrane of fritted glass displays, under a weak current, oscillations of water flux and of potentials. The calculations pertaining to this model can be generalised if the electroosmotic water flux is assumed in increase the dielectric constant of the lipidic membrane. Thus the notion of an electroosmotic increase upon the dielectric constant of the membrane offers an alternative to the pore theory. Besides other phenomena show the role of low dielectric constants. The conductance of lipids containing coloured cations increase when subjected to illumination. The radiant energy absorbed then surpasses the association energy of ion pairs.
麻醉剂在脂质中的溶解性推动了对细胞膜非水相和脂质模型的探索。有人提出了人工磷脂双层。只有当它们与环状离子载体或特定物质（如蛋白质组分EIM）接触时，才会表现出离子导电性和兴奋性。然而，许多脂质物质会形成非双层膜，具有离子导电性和兴奋性，无需任何特定添加剂。只需要少量游离脂肪酸。这是通过阳离子交换进行渗透的条件。有色阳离子和阳离子药物会发生大量交换。Cu++、Hg++、吐根碱++阳离子具有非常高的交换系数，这些系数可以通过实验测量，并且可以解释它们各自的抗真菌、抗菌和抗阿米巴作用。文中讨论了膜兴奋的可能过程。首先是经典的孔道，这是K+和Na+转移所特有的以及它们的“门控”机制，因为细胞膜是双离子系统。人工膜是单离子系统。但最近的研究表明，轴突膜可以转化为单离子系统，轴突内外仅以Co++作为唯一阳离子。文中提出了关于兴奋过程的建议。a）假设存在一个对应于结构微小构象变化的单一能量屏障。b）膜可能是触变性的。一个外部阳离子穿透膜时会在其身后留下一串流动性区域，如果下一个阳离子紧密跟随，它们就可以穿透这个区域。如果它们相距很远（在小电场下），随着结构固化，离子电流很快就会停止。c）最有前景的建议是，膜中的阴离子固定电荷和阳离子形成静电结合的离子对。当介电常数增加时，这种离子对的解离，即导电性，会显著增强。这个过程可能是由进入的阳离子携带的水产生的，也就是通过电渗作用。这正是在特奥雷尔的膜振荡器中发生的情况，在该振荡器中，多孔玻璃模型膜在弱电流下显示出水通量和电位的振荡。如果假设电渗水通量会增加脂质膜的介电常数，那么与该模型相关的计算就可以推广。因此，膜介电常数因电渗作用而增加的概念为孔道理论提供了一种替代方案。此外，其他现象也表明了低介电常数的作用。含有有色阳离子的脂质在光照下其导电性会增加。吸收的辐射能随后超过了离子对的结合能。
