Formation of cell outgrowths by external force: a model study.

Cell outgrowth formation by a force applied to the external membrane was investigated. This extrinsic force, which is generated in a special chamber by an alternating current (AC) electric field (EF) of high frequency, pulls the membrane outwards. The force arises due to the redistribution of ions beneath the cell surface and is applied to the thin (10-20 A) undermembrane layer. This force is sufficient to generate cell-specific membrane protrusions of various types. The morphology of these protrusions in mouse embryo and human fibroblasts, and in mouse L cells, resembles that of the outgrowths that these cells form under normal physiological conditions. Ehrlich ascites tumour cells (which normally grow in suspension) in an AC EF form only thin short processes. Erythrocytes when subjected to EF treatment are not capable of producing processes at all. An aligned system of microfilaments was found in the outgrowths produced by mouse embryo fibroblasts. However, cytochalasin B, sodium azide + 2-deoxy-D-glucose, carbonyl-m-chlorphenylhydrazon + 2-deoxy-D-glucose, colcemid and incubation at 4 degrees C were not able to prevent the generation of processes in an EF. It is proposed that the morphology of cell protrusions is determined by the structure of the domains in the plasma membrane, rather than by active cytoskeletal reorganization. The experimental system that we developed provides an opportunity for studying the mechanical linkages of cytoskeletal elements with the plasma membrane.