Potassium Ion Dynamics Imaging through Supported Lipid Bilayers with Surface Plasmon Resonance Microscopy

We have developed an optical microscope
based on surface plasmon resonance (SPR) to observe the dynamics of
potassium ion (K+) concentrations. We formed a polyvinyl
chloride (PVC) film containing ionophores that trap K+ on
top of a gold film that excites surface plasmon. By measuring the
attenuated total reflection spectra when injecting pure water or K+ solution on the fabricated substrate, we confirmed that the
ionophore chelation reaction changed the PVC refractive index. Subsequently,
we constructed a custom-made optical system for SPR imaging, mounted
the substrate, and imaged the two-dimensional diffusion of K+ concentration changes when high concentrations of K+ solution
were injected onto the substrate. In addition, we formed supported
lipid bilayers on the substrate, mimicking cell membranes. Compared
with the movie without lipid bilayer formation, that with supported
lipid bilayers was confirmed to have taken longer time to increase
the concentration due to its shielding effect of K+. Finally,
we added K+ channels into the lipid bilayer membrane and
visualized a K+ diffusion using the same procedure as that
in the previous imaging experiment. We succeeded in observing the
dynamics of K+ concentration change through the K+ channels inserted in the lipid bilayer. The addition of K+ channels weakened the shielding effect and shortened the time required
for the K+ concentration to increase.