TABLE II.

Mechanisms of mechanical sensing in biological systems.

Force/energy	Examples	Main protein/structures involved	Magnitude of force/stress	Example References
Turgor pressure	Plant or fungal cell growth	Ion channels	MPa	84, 128, 82
Fluid shear stress	Blood flow in vasculature Urine flow in kidney	Primary cilium, glycocalyx	0.01–1 Pa	121, 129, 130, 131
Actomyosin contractility against viscoelastic substrates	Stresses at focal adhesions	Actomyosin/integrins/cytoskeletal linkers formation of catch bonds in cell-matrix linkers	50–100 000 Pa	132, 23, 127
Vibrations / sound	Hair cell protrusions in animals trichomes in plants	Acoustic waves bend actin bundles to put tension on tip links in ear cells or rotate trichrome structures in plant cells	>20 μPa	133, 134
Hydrostatic pressure	Hypertension, glaucoma, and arthritis	Cardiovascular function, balance of inflow and outflow in eye, brain, gravitational stress on joint fluid	0.2 kPa–5 MPa	135
Osmotic pressure	Cell and tissue swelling	Ion or water channels	kPa–MPa	19, 80
Solid stress	Compression of normal tissue by growing tumor	Deformation of neurons, constriction of blood flow	0.1–10 kPa	77
Tensile stresses in plants	Stretching of cell walls due to growth or internal pressure	Cellulose/pectin transmit stress to transmembrane proteins (channels/kinases) that alter function	10 s of MPa	136
Compressive stress in cartilage and bone	Compression at cartilage/bone interface of joints during walking	Collagen/glycosaminoglycan networks transmit force to alter cell membrane protein structure or expose cryptic binding sites. Induce flow in internal fluid channels	1–10 MPa	137, 138
Shear flow sensing	E. coli	FimH that comprises the adhesive tip pf type 1 pilus	0.2 Pa	139
Pressure or other forces generated by flow or motility bend, shear, or stretch the cell envelope	E. coli membrane proteins	Mechanosensitive channels, possibly CpxA/CpxR and NlpE	kPa	140, 141