The Mechanism of Activation of Piezo Ion Channels

Abstract

Piezo ion channels mediate the conversion of mechanical touch into electrical signals and are critical for the organism's responsiveness to mechanical forces. How Piezos detect mechanical stimuli is unknown.The apparent mechanical sensitivity of Piezo1 varies substantially across cellular environments, stimulating methods and protocols, raising the fundamental questions of what precise physical stimulus activates the channel and how its stimulus sensitivity is regulated. Here, we measured Piezo1 currents evoked by membrane stretch, while simultaneously visualizing and measuring membrane geometry. Building on this approach, we developed protocols to minimize resting membrane curvature and tension prior to probing Piezo activity. We find that Piezo1 responds to lateral membrane tension with high sensitivity as compared to other mechanically activated channels and that resting tension can drive channel inactivation, thereby tuning overall mechanical sensitivity of Piezo1. Our results explain how Piezo1 can function efficiently and with adaptable sensitivity as a sensor of mechanical stimulation in diverse cellular contexts.The next step in understanding the mechanism of Piezo activation would be the identification of structures within Piezos that detect a mechanical stimulus and that mediate channel inactivation. We hypothesized that specific structures within Piezos are highly sensitive to localized application of force, whereas others are less sensitive in comparison. To test this hypothesis, we developed a novel method, where we apply highly localized force to specific protein domains and simultaneously measure ion channel activity upon pressure-clamp stimulation. For this, we label specific domains within Piezos with magnetic nanoparticles and use an external magnetic field to generate a precise mechanical force that is highly localized. Simultaneously, we measure Piezo-activation electrophysiologically. With this approach we have identified domains that are sensitive to application of localized magnetic pulling force and other domains that are completely insensitive to the same force.