Detection of cation migration through gramicidin channels in membrane-sandwich sensor set-ups.

<p>Refractive indices (n_cTM) of the sensor-covering fluid layer were measured in the transverse magnetic (TM) mode in sensor set-ups containing empty or lipid-filled filter membranes (<b>A</b>, <b>B</b>) after injecting ethanolamine (<b>A</b>) or guanidine (<b>B</b>) solutions, and after the incorporation of gramicidin (<b>C</b>, <b>D</b>). The inserts show averages and standard deviations of n_cTM changes, calculated from three independent experiments. Significant (***p<0.001; paired <i>t</i>-test) differences were found in response to filling with liposomes regardless of the chemical nature of the analyte (<b>A</b>, <b>B</b>). Incorporation of gramicidin, while resulted in enhanced permeation of ethanolamine (<b>C</b>), did not cause detectable changes in the move of guanidine (<b>D</b>).</p

The minimum amount of detectable material in assays with various sensor set-ups.

<p>The minimum amount of detectable material in assays with various sensor set-ups.</p

Schematic view of the membrane-sandwich sensor set-up.

<p>A thick (140 µm) PTFE lipid-holder membrane was placed on the top of a thin (23 µm) PET membrane for complete separation of lipid material from the sensor surface.</p

Demonstration of Cl^–-channel functions of cell-derived GABA receptors in the membrane-sandwich sensor set-up.

<p>OWLS recordings were made in Cl^–-free ACSF as running buffer with injection of Cl^–-containing ACSF (ACSF) with or without GABA and the channel blocker bicuculline (ACSF+GABA and ACSF+GABA+Bic, respectively). (<b>A</b>) Changes of the effective refractive index (NTM) values in a representative OWLS assay. (<b>B</b>) Changes in the refractive index (n_cTM) in response to the GABA-channel blocker bicuculline are shown from a representative experiment. (<b>C</b>) Summary of refractive index (nc_TM) changes (Δnc_TM) in response to transfusion with Cl^–-containing buffer (ACSF), in the presence of the agonist GABA (ACSF+GABA) or in the presence of both GABA and the channel-blocker bicucullin (ACSF+GABA+bicucullin). Δnc_TM values were calculated from data of 4 independent series of experiments (n≥4); averages and standard deviations are presented.</p

OWLS recordings of deposition of multiple liposome layers and permeability for small organic cations.

<p>(<b>A</b>) Biotinylated sensors were treated with (1) NeutrAvidin; (2) biotin-ssDNA; (3) Chol-dsDNA1-tagged liposomes; (4) Chol-dsDNA2. The insert shows the increasing thickness (dA) of the deposited material on the surface reaching the detectable maximum (∼200 nm) after the second injection of liposomes. (<b>B</b>, <b>C</b>) Changes of the effective refractive indices (NTM) in a representative series of experiments with cross-linked multilayer of liposomes without (<b>B</b>) or with (<b>C</b>) gramicidin channels after injections of ethanolamine (5), methylamine (6) or guanidine (7) solutions.</p