Cell Spreading and Cell Movement: an Active or a Passive Process?

Abstract

THE mechanism of amoeboid movement in general, and more specifically that of tissue cells such as fibroblasts, is controversial and unknown. Most theories state that cell movement involves active changes in cell shape, brought about by forces generated by metabolic energy, such as pseudopod formation and withdrawal, but there is no agreement about the site and nature of the forces involved¹. In marked contrast to such theories, the recent theory put forward by Carter² for tissue cells suggests that cell motility is essentially a passive phenomenon wherein net forces are generated by asymmetric surface tension type forces at the interfaces between cell, substratum and surrounding medium. To test this theory for tissue cells a simple series of experiments has been carried out on the effect of temperature on the spreading and rounding up of cells. Most tissue cells, such as fibroblasts, when freed from contact with other cells or other solid substratum and maintained in suspension, become more or less rounded^3,4. When they are allowed to settle on a solid surface they tend to flatten on it; the question is whether this is brought about by active cellular processes or whether it is a passive phenomenon due to surface tension forces as Carter suggests. If cell spreading were caused by passive spreading, it ought not to be significantly affected by lowered temperature, which does, however, considerably reduce active cell movement.