MCAs in Arabidopsis are Ca2+-permeable mechanosensitive channels innately sensitive to membrane tension

Abstract Mechanosensitive (MS) ion channels respond to mechanical stress and convert it to electric and ionic signals that activate appropriate cellular mechanisms. Although the force-sensing mechanisms of MS channels remain obscure, the following have been proposed: activation by force from membrane lipids and activation by force delivered from associated proteins. Five MS channel families have been identified to date in plants, including the Arabidopsis thaliana Mid1-Complementing Activity (MCA) channel; however, their activation mechanisms have not yet been elucidated in detail. We herein demonstrated that the MCA2 channel is a Ca2+-permeable mechanosensitive channel that is directly activated by membrane tension. The N-terminal 173 residues of MCA1 and MCA2 were synthesized in vitro, purified, and reconstituted into artificial liposome membranes. Ca2+ fluorometry demonstrated that liposomes reconstituted with MCA1(1-173) or MCA2(1-173) mediated Ca2+ influx. The patch-clamp technique revealed that the application of pressure to the membrane reconstituted with MCA2(1-173) elicited channel currents. This channel was also activated by voltage. Blockers for mechanosensitive channels inhibited stretch, but not voltage, activation. Since MCA proteins are found exclusively in plants, these results suggest that MCA represents a plant-type MS channel that opens directly with membrane stretch.