16.12:
Mechanically-gated Ion Channels
Mechanically-gated ion channels are transmembrane proteins that open in response to various stimuli like pressure, touch, sound, and temperature.
Through these open channels, ions move down their electrochemical gradient depolarizing the membrane. This leads to the propagation of an action potential to the central nervous system to induce appropriate responses.
The most extensively studied PIEZO channels open in response to mechanical stress like touch and pressure. Interestingly, these channels respond not only to external stimuli but are also internal sensors for blood pressure regulation and breathing.
Another type, TRP ion channels, have a broad role in sensory perception. On touching a hot surface, TRPV1, a temperature-gated ion channel at the nerve ending, opens. Sodium and calcium ions pass through this open channel, changing the nerve fibers' membrane potential. This generates an action potential that travels to the brain, triggering a painful and burning sensation.
16.12:
Mechanically-gated Ion Channels
Mechanically-gated ion channels are proteins found in eukaryotic and prokaryotic cell membranes that open in response to mechanical stress. Tension, compression, swelling, and shear stress can alter the conformation of the protein, opening a transmembrane channel that allows the passage of ions for signal transmission. In eukaryotes, mechanically-gated channels are distributed in several regions like the neurons, lungs, skin, bladder, and heart, where they play critical roles in numerous physiological and pathophysiological processes.
In 2021 the Nobel Prize in Physiology or Medicine was awarded to David Julius and Ardem Patapoutian for their discovery and advancement of the knowledge of mechanically-gated ion channels, TRP, and Piezo channels.
David Julius discovered the presence of transient receptor potential (TRP) channels are expressed in many cell types and tissues. Some members of this large family of proteins act like thermometers involved in hot and cold sensations. Like the TRPV1, it gets activated by several factors such as temperature higher than 43 ℃, allyl isothiocyanate found in wasabi and mustard, and capsaicin, the hot component of peppers. So when we eat something spicy, the intense heat generated causes sweating. This is because the channel gets activated by capsaicin, allowing sodium and calcium ions to flow through it into the cell. This triggers electrical activity that sends messages of spice sensation and pain to the brain.
Ardem Patapoutian worked on the Piezo channels, the novel class of mechanosensitive ion channels. He discovered that these channels are required for the perception of touch and proprioception. Abnormalities in the functioning of these channels can cause muscular and neuronal degeneration, cardiac myopathies, hypertension, and cancer. In certain cancers, the upregulation of Piezo channels allows calcium ions influx, thereby modulating key calcium-dependent signaling pathways associated with cancer progression.
Suggested Reading
- Ranade, Sanjeev S., Ruhma Syeda, and Ardem Patapoutian. "Mechanically activated ion channels." Neuron 87, no. 6 (2015): 1162-1179.
- Delmas, Patrick, and Bertrand Coste. "Mechano-gated ion channels in sensory systems." Cell 155, no. 2 (2013): 278-284.
- Martinac, Boris. "Mechanosensitive ion channels: molecules of mechanotransduction." Journal of cell science 117, no. 12 (2004): 2449-2460.