Lipid Bilayer Experiments with Contact Bubble Bilayers for Patch-Clampers. 
Lipid bilayers provide a unique experimental platform for functional studies of ion channels, allowing the examination of channel-membrane interactions under various membrane lipid compositions.  Among them, the droplet interface bilayer has gained popularity; however, the large membrane size hinders the recording of low electrical background noise.  We have established a contact bubble bilayer (CBB) method that combines the benefits of planar lipid bilayer and patch-clamp methods, such as the ability to vary the lipid composition and to manipulate the bilayer mechanics, respectively.  Using the setup for conventional patch-clamp experiments, CBB-based experiments can be readily performed.  In brief, an electrolyte solution in a glass pipette is blown into an organic solvent phase (hexadecane), and the pipette pressure is maintained to obtain a stable bubble size.  The bubble is spontaneously lined with a lipid monolayer (pure lipids or mixed lipids), which is provided from liposomes in the bubbles.  Next, the two monolayer-lined bubbles (~50 µm in diameter) at the tip of the glass pipettes are docked for bilayer formation.  Introduction of channel-reconstituted liposomes into the bubble leads to the incorporation of channels in the bilayer, allowing for single-channel current recording with a signal-to-noise ratio comparable to that of patch-clamp recordings.  CBBs with an asymmetric lipid composition are readily formed.  The CBB is renewed repeatedly by blowing out the previous bubbles and forming new ones.  Various chemical and physical perturbations (e.g., membrane perfusion and bilayer tension) can be imposed on the CBBs.  Herein, we present the basic procedure for CBB formation.