The transduction of very small hydrostatic pressures

This paper reviews experiments in which cells, subjected to hydrostatic pre ssures of 20 kPa or less, (micro-pressures), demonstrate a perturbation in growth and or metabolism. Similarly, the behavioural responses of aquatic a nimals (lacking an obvious compressible gas phase) to comparable pressures are reviewed. II may be shown that in both cases the effect of such very lo w hydrostatic pressures cannot be mediated through the thermodynamic mechan isms which are invoked for the effects of high hydrostatic pressure. The ge neral conclusion is that cells probably respond to micro-pressures through a mechanical process. Differential compression of cellular structures is li kely to cause shear and strain, leading to changes in enzyme and/or ion cha nnel activity. If this conclusion is true then it raises a novel question a bout the involvement of 'micro-mechanical' effects in cells subjected to hi gh hydrostatic pressure. The responses of aquatic animals to micro-pressure s may be accounted for, using the model case of the crab, by the mechanical , bulk, compression of hair cells in the statocysts, the organ of balance. If this is true, it raises the interesting question of why the putative cel lular mechanisms of micro-pressure transduction appear to have been superse ded by the statocyst. (C) 1999 Elsevier Science Inc. All rights reserved.