Mechanosensitive channels

Mechanosensitive channels, mechanosensitive ion channels or stretch-gated ion channels are membrane proteins capable of responding to mechanical stress over a wide dynamic range of external mechanical stimuli. They are present in the membranes of organisms from the three domains of life: bacteria, archaea, and eukarya. They are the sensors for a number of systems including the senses of touch, hearing and balance, as well as participating in cardiovascular regulation and osmotic homeostasis (e.g. thirst). The channels vary in selectivity for the permeating ions from nonselective between anions and cations in bacteria, to cation selective allowing passage Ca²⁺, K⁺ and Na⁺ in eukaryotes, and highly selective K⁺ channels in bacteria and eukaryotes.

All organisms, and apparently all cell types, sense and respond to mechanical stimuli. MSCs function as mechanotransducers capable of generating both electrical and ion flux signals as a response to external or internal stimuli. Under extreme turgor in bacteria, non selective MSCs such as MSCL and MSCS serve as safety valves to prevent lysis. In specialized cells of the higher organisms, other types of MSCs are probably the basis of the senses of hearing and touch and sense the stress needed for muscular coordination. However, none of these channels have been cloned. MSCs also allow plants to distinguish up from down by sensing the force of gravity. MSCs are not pressure-sensitive, but sensitive to local stress, most likely tension in the surrounding lipid bilayer.

Mechanosensitive channels were discovered in 1983 in the skeletal muscle of the chick by Falguni Guharay and Frederick Sachs. They were also observed (pub. 1986) in Xenopus oocytes, and frequently studied since that time. Since then, MS channels have been found in cells from bacteria to humans: they are now known to be present in all three domains of life (Archaea, Bacteria and Eukarya, incl. plants and fungi). In the decades since the discovery of MS, the understanding of their structure and function has increased greatly, and several have been cloned. Specifically, the cloned eukaryotic mechanosensitive channels include the K⁺ selective 2P domain channels and the recently cloned cation selective PIEZO family.

MS can be classified based on the type of ion to which they are permeable.

Cation Selective MSCs: As the name suggests, they exhibit a selective permeability for positive ions with the most selective channels being those for K⁺. The most common eukaryotic MSCs are cation selective passing Na⁺, K⁺ and Ca²⁺ but not Mg²⁺. They have a single channel conductance range (25-35 pS) and they are blocked by trivalent ion Gadolinium. The K⁺ selective MSCs such as TREK-1 are not blocked by Gd³⁺.

Anion Channels: they exhibit a significant permeability for negative ions, and are not predominant as cation MS. They have a large conductance range (> 300pS).

...
Wikipedia