Asymmetric mechanosensitivity in a eukaryotic ion channel

Abstract

Living organisms perceive and respond to a diverse range of mechanical stimuli. A variety of mechanosensitive ion channels have evolved to facilitate these responses, but the molecular mechanisms underlying their exquisite sensitivity to different forces within the membrane remains unclear. TREK-2 is a mammalian twopore domain (K2P) K + channel important for mechanosensation, and recent studies have shown how increased membrane tension favors a more expanded conformation of the channel within the membrane. These channels respond to a complex range of mechanical stimuli, however, and it is uncertain how differences in tension between the inner and outer leaflets of the membrane contribute to this process. To examine this, we have combined computational approaches with functional studies of oppositely oriented single channels within the same lipid bilayer. Our results reveal how the asymmetric structure of TREK-2 allows it to distinguish a broad profile of forces within the membrane, and illustrate the mechanisms that eukaryotic mechanosensitive ion channels may use to detect and fine-tune their responses to different mechanical stimuli.any forms of sensory perception in higher organisms depend on the rapid conversion of mechanical and physical stimuli into the electrochemical language of nerve and muscle cells (1). These transduction mechanisms often involve "mechanosensitive" (MS) ion channels that are able to rapidly convert physicomechanical stimuli into the electrical signals required for complex physiological responses (e.g., touch, pain, hearing, proprioception), as well those mechanical signals that play key roles in development and cell-cell communication (2). The enormous complexity and diversity of these sensory responses suggests that a variety of molecular mechanisms are likely responsible; for example, while some channels are regulated via physical coupling to proteins of the cytoskeleton and/or cell matrix, others respond directly to changes in lipid membrane tension (3). The precise structural and physical mechanisms underlying these processes remain poorly understood, however (4-6).Our current understanding of how membrane tension directly regulates ion channel gating is largely derived from studies of prokaryotic MS ion channels involved in the control of bacterial turgor pressure (7,8). The open state of these MS channels has a larger cross-sectional area than the closed state within the membrane, and stretch-induced changes in the forces within the bilayer stabilize the expanded open-state conformation. This is commonly referred to as the force-from-lipid principle of mechanosensitivity (9). Similar physical principles are thought to regulate many eukaryotic MS channels (5, 10).Typically, the functional activity of MS ion channels is examined in pipette-based patch-clamp recordings in which negative or positive pressures are used to alter bilayer tension. These pressure changes stretch the membrane to alter the lateral pressure profile, the complex profile of forces that vary with location acro...

β1 subunit stabilises sodium channel Nav1.7 against mechanical stress

“…; Clausen et al . ). In our study, we therefore applied the mechanical stimulus by using the flow of a perfusion system.…”

Reconstitution and Electrophysiological Characterization of Ion Channels in Lipid Bilayers

“…If the solution appears as a white deposit, it may be due to water in the lipid solution. Concentrations of D-sorbitol ranging from 210 mM to 1 M can be used (Clausen, Jarerattanachat, Carpenter, Sansom, & Tucker, 2017;Kumar, Das, Schütte, Steinem, & Dash, 2016). An osmolarity of 380 mOsm works well with the K200 recordings solution.…”

“…This value was determined for Kv11.1, Kv7.1, Slick, and Slack channels (Tejada et al, 2017). For purified TREK-2 a final concentration of 1 to 5 ng/µl is employed (Clausen et al, 2017), and for the bacterial Klaerke et al…”

“…A temperature control unit may be added to test thermosensitivity . The suction control unit makes it possible to address mechanosensitivity of reconstituted channels (Aryal et al, 2017;Clausen et al, 2017).…”

“…Other amplifiers, such as the Axiopatch 200B connected to the Port-a-Patch via a Digidata 1440A digitizer (Molecular Devices) may be employed as well (see Aryal et al, 2017;Clausen et al, 2017).…”