Science Topics – 177

Programmable tension-clamp apparatus for studying tension-sensitive channels

Yuka Matsuki (Masayuki Iwamoto, Shigetoshi Oiki)

Membrane tension significantly influences the function of membrane proteins. We have previously analyzed the tension sensitivity of ion channels using single-channel current recordings in contact bubble bilayers (CBBs), which are formed by lipid monolayers at the surface of water droplets in oil. While the CBB method allows for tension control by adjusting the bubble pressure, maintaining a constant tension requires exact pressure regulation using a microinjector, demanding substantial experimental expertise. In this study, we developed a system that enables real-time measurement of membrane tension based on the Young-Laplace and Young equations, using microscopic images of bubbles (bubble radius and contact angle between bubbles) and pressure values. Additionally, we implemented a feedback control system that automates the operation of the microinjector. This system allows for stable long-term maintenance of membrane tension and enables rapid and accurate adjustment to desired tension levels. Using this innovative approach, we achieved unprecedented precision in analyzing the tension dependence of KcsA and TREK channels. This device is expected to become a new standard method for studying ion channel tension sensitivity and contribute to the automation and efficiency of such experiments.

Programmable Lipid Bilayer Tension–Control Apparatus for Quantitative Mechanobiology.
Yuka Matsuki, Masayuki Iwamoto, Takahisa Maki, Masako Takashima, Toshiyuki Yoshida, Shigetoshi Oiki. ACS nano: 2024, vol.18, issue 44, p.30561-30573.

＜Figure Legends＞
A representative tension-clamp experiment for the tension-sensitive KcsA potassium channel. The KcsA channel was reconstituted into a CBB, and membrane tension was set programmed in advance as a staircase up and down pattern ranging from 3 to 8 mN/m (red). A single-channel current trace with seven channels in the membrane at +200 mV shows reproducible and reversible changes in open probability upon stepwise tension changes. Current traces in the expanded time scale indicate that each channel responded to the tension independently.

Department of Anesthesiology and Reanimatology, Faculty of Medical Sciences, University of Fukui, Fukui, Japan.
Department of Molecular Neuroscience, Faculty of Medical Sciences, University of Fukui, Fukui, Japan.
Biomedical Imaging Research Center, University of Fukui, Fukui, Japan.