Electrochemical Analysis of Ion Channels and Transporters in Pore-Suspending Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 322

sistance as this system allows the flux of ions from the cis to the
trans compartment and vice versa. Of note, the discussion of sta-
tionary currents is based on the hypothesis that only the membrane
conductance G m of the nano-BLMs is modulated by CCCP,
whereas the conductive properties of the crystal-like PM-
fragments G p is unaffected. Hendler et al. 102 were able to show that
PM-fragments are, however, indeed permeabilised by CCCP.
Hence, the analysis of the stationary current following Eq. (28)
might be too simplistic and needs to be improved. Another point of
discussion is the observation that the stationary current reaches
saturation at a CCCP-concentration of about 70 μM ( Fig. 20 B ).
To elucidate this observation, we simulated I stat based on Eq. (13).
For I p,0 , V * and G m , values were kept constant, while G p was varied
in a range of 10 -4 - 10 -9 S. In the case of G p << G m , the stationary
current I stat reaches a maximum value. For G p >> G m , however, I stat
goes to zero. The most significant change of I stat is observed for G m
in a range of 10 -5 - 10 -6 S. This matches the ratio of I p,0 and V * . We
reason that the maximum value of the stationary current observed
in photocurrent measurements on PM-fragments in the sandwich
configuration depends on the intrinsic parameters I p,0 and V * .

3. Insertion of bR in Pore-Spanning Membranes

The ultimate goal is to reconstitute a transporter protein into a
pore-spanning membrane by fusing and spreading proteoliposomes
to obtain large protein densities. For the experiments described in
this chapter, the setup depicted in Fig. 1 B was used with partially
open alumina pore arrays. Similar to the protocol used for the re-
constitution of gramicidin into pore-suspending membrane, first a
bilayer is formed on the functionalized porous alumina substrate
followed by the incubation with bR-containing liposomes, which
were prepared by the reversed phase method. 103 The vesicles were
composed of DPhPC/DOPC/1,2-dipalmitoyl- sn -glycero-3-
phosphate (DPPA) (6:3:1) doped with 1 mol% bR. It is known that
the negatively charged headgroups of DPPA enhance the photo-
currents. 104 Prior to the addition of bR-containing vesicles, control
experiments were performed to rule out any photoartefacts. The
electrical characterisation of the system prior to and after the addi-
tion of the proteoliposomes was performed using EIS. The light-
induced proton pumping activity was detected by platinised plati-