Table 2.

Summary of experimental evidence regarding cell excitation by means of hydrostatic pressure application

References	Cell type	Pressure magnitude	Pressure frequency	Observed effects
Imamura et al. (1990)	Osteoblast-like MC3T3-E1 cells	0.5–2 atm	Static	Inhibition of osteoblast differentiation, promotion of osteoclast production (“optimum” pressure: 100 kPa), increased PGE synthesis
Ozawa et al. (1990)	Mouse osteoblast-like MC3T3-E1 cell	1 and 3 atm	Continuous	Decreased osteoblast numbers, increased PGE2 expression
Klein-Nulend et al. (1995)	Osteocytes from chicken calvariae	13 kPa	0.3 Hz (1 s loading, 2 s relaxation), for 24 h	Increase in prostaglandin release (can enhance bone formation)
Roelofsen et al. (1995)	Neonatal mouse calvarial cells	13 kPa	0.3 Hz	Stimulation of osteoblastic activity, stimulation of actin expression, AP activity
Brighton et al. (1996)	Calvarial bone cells from neonatal rats, exhibiting an osteoblast phenotype	17.2–69 kPa	1 Hz, for 10 cycles	increased proliferation, increased cytosolic calcium concentration
Vergne et al. (1996)	ROS 17/2.8 (rat osteoblast-like cells)	50–90 kPa	1 and 0.1 Hz, 20 min test duration	Increase in cell saturation density (for a frequency of 1 Hz), decreases alkaline phosphatase activity
Rubin et al. (1997)	Marrow cells from tibiae and femurs of C57BL/6 mice	1–2 atm	Static	Decreased osteoclast formation, decrease in mRNA coding for the membrane-bound form of MCSF
Nagatomi et al. (2001)	Osteoblasts from the calvaria of neonatal rats	10–40 kPa	0.25 or 1 Hz, 1 h daily	Elongated pressure decreases osteoblast proliferation, the same pressure stimulus causes different effect on different cells
Nagatomi et al. (2002)	Bone marrow cells (source of osteoclasts) from rat femurs	10–40 kPa	1 Hz (sinusoidal wave form), for 1 h per day	Reduced osteoclast differentiation and resorption activity, lower concentration of IL-1$\mathit{\alpha }$, down-regulation of mRNA expression for IL-1$\mathit{\alpha }$, IL-1$\mathit{\beta }$, and TNF-$\mathit{\alpha }$
Nagatomi et al. (2003)	Osteoblasts isolated from rat calvariae	10–40 kPa	1 Hz, for 1 h daily	Increased type-I collagen mRNA expression, increased amount of acid-soluble collagen, increased calcium concentration
Takai et al. (2004)	Primary osteoblasts obtained from trabecular bone cores taken from the epiphyses of metacarpal bones from 3- to 4-month-old calves	3 MPa	0.33 Hz (triangle wave form), for 1 h/day	Increased osteoblast function (only when osteocytes are present), increased osteocyte viability
Maul et al. (2007)	Bone marrow progenitor cells from rats	10–16 kPa	1 Hz	Enhanced proliferation
Gardinier et al. (2009)	MC3T3 osteoblast-like cells	0–68 kPa	0.5 Hz	Increased anabolic response, increase in ATP release, increased COX-2 levels
Liu et al. (2009)	Bone marrow stromal cells from tibiae and femurs of rats	10–36 kPa	0.25 Hz (sinusoidal wave form)	Increase in osteoblast activity-related transcription factors
Liu et al. (2010)	MLO-Y4 osteocyte-like cells (i.e., deriving from cells extracted from transgenic mice)	68 kPa	0.5 Hz (triangular wave form), for 1 or 2 h	Decreased osteocyte apoptosis, increase in intracellular calcium (after 40 s, may be related to osteoblast activity), of RANKL/OPG ratio (after 2 h), and of COX-2 mRNA level (after 1 h)
Rottmar et al. (2011)	Human bone- derived cells, from the hip marrow	1–11 kPa	30 min stimulation, 7 h, 30 min break	Increased osteogenic differentiation and proliferation
Henstock et al. (2013)	Cells contained in whole femurs of chick foetuses	0–279 kPa	0.0001–2 Hz	Increased volume of diaphysial collar