Electrochemical Analysis of Ion Channels and Transporters in Pore-Suspending Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 306

Table 1
Ratio of the Diffusion Coefficients D J 0.5 /D I 0.5 of Two Alkali Cat-
ions. The Experimental Values were Determined from the
Slopes of the Linear Regressions to the Data Shown in Fig. 14
B . The Theoretical Values are Based on the Diffusion Coeffi-
cients in Aqueous Solution.

I + / J +

Experimental Theoretical

K + / Na +

0.89 0.83

Na + / Li + 0.74 0.88

K + / Li + 0.66 0.72

valent cations. Others, who investigated ion transport processes on
gallium-arsenide-supported membranes included, in addition to a
Warburg-element, a RC -circuit, which accounts for the properties
of the underlying electrode. 85 In most studies that deal with ion
channel-doped SSMs, only the properties of the supporting elec-
trode is included, while the mass transport is neglected. 12,77

( iii ) Gramidicin Transfer from Peptide-Doped Liposomes to
Pore-Spanning Lipid Bilayers

The success of the reconstitution protocol is the transfer rate
of the peptide from the vesicles into the pore-suspending mem-
branes. To investigate the kinetics of the gramicidin transfer in
more detail, gramicidin-doped liposomes were prepared in alkali
cation-free buffer and added to a pore-suspending membrane in the
presence of KCl. Gramicidin itself serves as an indicator for its
insertion, as a conductance change is only observed if it is inte-
grated in the pore-spanning bilayer. As a control, the same exper-
iments were carried out with gramicidin-free vesicles. Impedance
spectra were taken in intervals of 30 min and the membrane re-
sistance R a was extracted using the equivalent circuit from Fig. 7 C
(in the absence of KCl) and Fig. 13 D (in the presence of KCl).
The change in conductance ǻ G = G ( t ) - G ( t = 0), plotted as a func-
tion of time ( Fig. 15 ), demonstrates that only in the presence of
gramicidin-doped vesicles an almost exponential increase in con-
ductance is observed, while in the control experiment no increase
in conductance was monitored.