59 - Effects of High Pressure on Cellular Processes

Abstract

This chapter discusses that high hydrostatic pressure affects equilibria and reaction rates through the molar volume changes involved in the reaction system as a whole. The chapter explains how high hydrostatic pressure affects molecules of biological interest, and their interactions; the ways in which pressure affects cellular processes; and how animals, including humans are affected by pressure. Along with high pressure, the chapter also intends to stimulate interest in a particular approach to physiology. The discussion on molecular effects of pressure and temperature includes equilibrium processes in aqueous solution, lipid bilayers under pressure and rates of chemical reactions. It is mentioned that hydrostatic pressure is not directional and that osmotic pressure is also quite separate from hydrostatic pressure. Hydrostatic pressure is a force acting in all directions, in the air one breathes, in water, or in body fluids. While high pressure, surprisingly perhaps, dissociates molecules in aqueous solution, it has the intuitively expected effect on lipid bilayers, compressing and ordering their structure. The thermodynamics of equilibrium processes in aqueous solution, and the phase state of lipid bilayers at high pressure, inevitably fall short of explaining how pressure affects rates of reaction. Muscle, a tissue whose cells are conspicuously filled with polymerized proteins, is affected by high pressure in ways determined by the contraction cycle. Simple processes, such as the diffusion of gases or water in aqueous solution, are little affected by the pressure range of interest here. Chondrocytes are cells, which synthesize the load-bearing extracellular matrixthat covers the articulating surfaces of joints. The buoyancy of aquatic animals subjected to significant pressure is interesting because buoyancy requires the creation of a void or region of low-density, working against the ambient pressure. Animals and bacteria live at high pressures in the deep sea, down to the greatest depths where the pressure is approximately 100 MPa. Several technological applications have arisen from high pressure biology—the manipulation of ploidy, and of membrane proteins; sterilization and inactivation of microorganisms; food processing; and safe human diving.