Abstract
Abstract The permeation of the lipophilic ion dipicrylamine through planar lipid membranes formed from dipalmitoylphosphatidylcholine in n -decane shows an anomaly near the main phase transition of this system. Both the rate constant, k i , of ion translocation across the membrane interior and the interfacial concentration, N , of this ion have a maximum at about 36°C. Analogous experiments were performed with tetraphenylborate. A considerably lesser effect of the phase transition was found. The addition of cholesterol leads to a broadening of the maxima for k i and N . The time course of the current following a voltage jump shows a characteristic change below a temperature of about 45°C, if the molar ratio cholesterol/ phosphatidylcholine in the membrane forming solution exceeds 1. While the current transient decays exponentially above 45°C, a sum of two exponential terms yields an adequate fit below that temperature. This is regarded as evidence for a lateral phase separation below 45°C into structurally different domains, which provide two different pathways for dipicrylamine.
Published Version
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