The biological membrane is not just a platform for information processing but also a field of mechanics. The lipid bilayer that constitutes the membrane is an elastic body, generating stress upon deformation, while the membrane protein embedded therein deforms the bilayer through structural changes. Among membrane-protein interplays, various channel species act as tension-current converters for signal transduction, serving as elementary processes in mechanobiology. However, in situ studies in chaotically complex cell membranes are challenging, and characterizing the tension dependency of mechanosensitive channels remains semiquantitative owing to technical limitations. Here, we developed a programmable membrane tension-control apparatus on a lipid bilayer system. This synthetic membrane system [contact bubble bilayer (CBB)] uses pressure to drive bilayer tension changes via the Young-Laplace principle, whereas absolute bilayer tension is monitored in real-time through image analysis of the bubble geometry via the Young principle. Consequently, the mechanical nature of the system permits the implementation of closed-loop feedback control of bilayer tension (tension-clamp CBB), maintaining a constant tension for minutes and allowing stepwise tension changes within a hundred milliseconds in the tension range of 0.8 to 15 mN·m-1. We verified the system performance by examining the single-channel behavior of tension-dependent KcsA and TREK-1 potassium channels under scheduled tension time courses prescribed via visual interfaces. The result revealed steady-state activity and dynamic responses to the step tension changes, which are essential to the biophysical characterization of the channels. The apparatus explores a frontier for quantitative mechanobiology studies and promotes the development of a tension-operating experimental robot.
Keywords: TREK-1 channels; contact bubble bilayer; feedback control; flicker gating; imaging; lipid bilayer; membrane tension.