Interpreting ion fluxes to channel arrays in monolayers

Abstract

The exponentially decaying permeability model interprets the chronoamperometric currents arising from Tl+ reduction at a Hg electrode covered with a phospholipid monolayer (DOPC) containing gramicidin monomer by combining three processes: (i) the diffusion of an ion to a membrane surface with an array of channels, (ii) the conformational dynamics of the individual channels, and (iii) the passage of the ion through the channels. The introduction of a variable permeability allows us to uncouple the diffusion from the heterogeneous processes, given that the concentration of a species at the active surface can be obtained by semi-integration of the currents. Consideration of a reverse step for the dehydration process at the mouth of the channel allows the analysis of potential steps away from diffusionlimited conditions where a Nernstian-like behavior of the relevant parameter is observed. The model has been successfully applied to data with all trans retinol or benzo-R-pyrene as additive to the phospholipid monolayer and to monolayers without any additive at all.

The authors gratefully acknowledge support of this research by BBMO #005199 FP6-2003-LifeSciHealth-Specific Action Support, by the Spanish Ministry of Education and Science (Projects CTQ2006-14385 and CTM2006- 13583), and from the “Comissionat d’Universitats i Recerca de la Generalitat de Catalunya”.