Hydrostatic Pressure in Metazoan Cells in Culture: Its Involvement in Locomotion and Shape Generation

Abstract

Internal hydrostatic pressure in bacteria and in plant cells is a main factor determining shape and growth of individual cells and multicellular organisms (cf. Chap. IV.1). The question whether osmotic pressure in animal cells also differs from that of the extracellular fluid is still unresolved. While a difference is obvious for freshwater protists, it is doubtful for cells of multicellular organisms. Erythrocytes of various species and eggs of some marine invertebrates, chick heart fibroblasts, and frog muscle cells all seem to behave roughly like osmometers (Dick 1959, 1966; Olmstead 1966). Doerner (1967) has postulated the occurrence of an internal pressure linked with the uniformly varying modulus of elasticity from the periphery of a cell toward its center. This pressure may vary from point to point on a cell surface and could well be involved in modeling cell shape. More recently, experimental evidence has accumulated showing that cellular behavior in hypotonic media differs considerably from that of an ideal osmometer (i.e. Skalak and Shu Chien 1982; Roti Roti and Rothstein 1973; Raaphorst and Kruuv 1979). Any volume change which is not in accord with Boylè-van’t Hoff s law (deviation from an ideal osmometer) can be due to one of the following factors acting either alone or in accord with each other:

• 1. presence of an osmotically inactive part of the volume;

• 2. restricted mobility of the cell water;

• 3. release or uptake of ions, or other solutes;

• 4. osmotic activity of cytogel;

• 5. presence of an active force adding to osmotic pressure.