Mechanosensitive ion channels, also called mechanically activated ion channels, are a type of ion channels activated by mechanical forces such as pressure or stretch applied to the cell membrane. These channels are found in the cells of various organisms, from bacteria to humans, and have a wide range of biological functions. In bacteria, they help regulate osmotic pressure and are important for survival in changing environments. In plants, they are involved in processes like stomatal regulation and root growth. In animals, they play roles in hearing, sensing touch, proprioception, and the proper development of tissues and organs during embryogenesis.
Recent advances have significantly expanded our understanding of mechanosensitive ion channels, revealing a remarkable diversity in structure and function. Several ion channel families have been implicated in mechanotransduction to date:
PIEZO Channels: PIEZO1 and PIEZO2 have been extensively characterized and are known for their roles in mechanotransduction processes, including touch, mechanical allodynia, and blood pressure sensing. These channels are large, trimeric proteins with a distinctive structure contributing to their mechanosensitive functions.
MscL and MscS Channels: Originating from prokaryotes, these channels respond to osmotic shock by allowing ions and osmolytes to pass through, preventing cell lysis. Their structures and mechanisms of action have been well-studied, providing insights into their roles in bacteria and plants.
K2P Channels (TREK-1, TREK-2, and TRAAK): These two-pore potassium channels are inherently mechanosensitive and contribute to the cellular response to a variety of mechanical stimuli, including, poking, swelling, and stretching, as well as to temperature and various chemicals.
OSCA/TMEM63 Channels: Identified in both plants and animals, these channels have been validated as stretch-activated ion channels, with roles in various cellular responses to mechanical stress and osmotic conditions.
MET Channel: The mechanoelectrical transduction (MET) channel, with TMC1 and TMC2 as its pore-forming subunits, in auditory hair cells is essential for converting acoustic stimuli into electrical signals, thereby enabling hearing.
NOMPC: A mechanically activated TRP channel playing a key role in mechanosensory organs of Drosophila, C. elegans, and zebrafish (no mammalian homologs).
In addition to these ion channels, whose role has been confirmed, other channels have also been proposed to be involved in mechanotransduction, but their role has not yet been fully confirmed. These are:
DEG/ENaC and ASIC Channels: Although related to mechanotransduction, direct evidence for mechanosensitivity in mammals remains elusive. Their involvement in processes like blood pressure sensing and nociception suggests potential mechanosensitive functions.
TRP Channels: Several TRP channel family members are implicated in mechanosensory processes; however, direct activation by mechanical stimuli is conclusively shown only for NOMPC. The role of mammalian TRP channels in mechanosensation, particularly TRPV4, is supported by indirect evidence and requires further confirmation.
TACAN and Elkin Channels: These recently proposed families of mechanically activated ion channels represent exciting areas for future research. Their exact roles in mechanotransduction are still under investigation, highlighting the ongoing discovery process in this field.
This diversity underscores the complexity of mechanotransduction mechanisms across life forms, with each channel family contributing uniquely to the ability of organisms to respond to mechanical forces. As research progresses, the functional roles of these channels are expected to be further clarified, enhancing our understanding of their contributions to physiology and disease.
Techniques to study mechanically activated ion channels are varied and sophisticated, reflecting the complexity of mechanotransduction phenomena. Patch clamp technique remains a cornerstone for studying mechanically activated channel activity, allowing for the direct measurement of ion flow in response to mechanical stimuli. Mechanical force application methods, from fluid shear stress and cell swelling to membrane stretch and indentation, mimic physiological stimuli, helping to elucidate the channels' roles in cellular contexts.
Modern automated patch clamp platforms (Patchliner and SyncroPatch 384) now allow for studying mechanically activated ion channels using both mechanical and chemical stimulation in a high-throughput manner. These platforms allow for high-speed solution application to cells, providing a robust method for studying mechanosensitive channel activity under mechanical stress.
PIEZO1 channels are crucial for sensing mechanical forces, and their impaired function is linked to various pathophysiological conditions making PIEZO channels vital for drug discovery. High-throughput automated patch clamp (APC) using chemical activators such as Yoda1 has been used, but solely mechanical stimulation (M-Stim) and APC were so far unavailable for PIEZO1 channels. A recent study by Murciano et al. shows optimization of a high-throughput APC assay on SyncroPatch 384 with multihole NPC-384 chips, enabling M-Stim in high-throughput electrophysiology. Activating PIEZO1 channels by M-Stim on SyncroPatch 384 requires applying solutions at elevated pipetting flows. The ability to compare mechanical and chemical stimulation in high-throughput patch clamp assays is crucial for PIEZO1 channel investigations, offering a valuable tool for drug development.
Figure explains mechanical stimulation (M-Stim) on the SyncroPatch 384. The schematic illustration depicts a cross-section of one well of an NPC-384 chip. M-Stim delivers a small volume of solution locally to the cell (1 and 2) and uses an aspiration step (3, dashed arrows) to recover the dispensed volume. On the right, the top view of one well of an NPC-384 chip with 1 patch hole (1x) and 4 patch holes (4x) is shown. Representative PIEZO1 raw traces of single cells elicited by M-Stim at 40µl/s (light blue trace), 60µl/s (blue trace) and 110µl/s (dark blue trace) and blocked by GdCl3 (black trace) for mPIEZO1 (left), hPIEZO1 (middle) and untransfected cells (right).
We provide a range of electrophysiology platforms to study ion channels in native and heterologous cells and membranes:
These platforms can be used to study basic mechanisms of ion channel function, their role in cellular physiology, effects of patient and disease-derived mutations (channelopathies), and screen for new drugs.