The study of peptide ion channels by electrochemical techniques

Abstract

The synthesis of the gramicidin A (gA) analogue gram-2-(nicotinamido)ethyl carbamate (gAN) has been performed. Like gA itself, monomers of the nicotinamide analogue undergo self-assembly in lipid membranes to form K+ selective transmembrane ion channels. Scanning electrochemical microscopy (SECM) has been used to monitor the movement of permeable ions across these channels under a range of physiological conditions. Feedback curve results suggest that K+ ions only pass across the channels when a certain external potential, referred to as the switching potential, is applied to the membrane. This implies that ion transport in the system is controlled by the redox properties of the nicotinamide sub-unit, which acts as a pendant able to occlude the channel opening in the 'ball and chain' model of inactivation. Chronoamperometric measurements demonstrate that the gAN channel can be repetitively cycled between the opened and closed states. This controllable, predictable switching behaviour has possible applications in membrane transport and drug delivery systems. The permeability of gAN channels to Tl+ and Eu 3+ ions has also been tested by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with gold electrode supported lipid bilayers. Results indicate that the channel is permeable to the Tl+ ion although not to the multicharged Eu3+ ion, which is believed to bind occluding the channel entrance. It was also possible to directly monitor the passage of Tl+ ions across the gAN channel by using Prussian Blue as a dual-purpose electrolyte and electrochromic indicator.