F-actin organization influences the osmotic reactions of animal cells.

The resistance of chick embryo fibroblasts (CEF) and Ehrlich ascites tumour (EAT) cells to the disruption in strongly hypotonic medium was measured in the presence or absence of cytochalasin B. The osmotic resistance of CEF spread on solid substratum was much higher than that of CEF suspended in a fluid medium. Cytochalasin B decreased the osmotic resistance of spread CEF, but not of suspended CEF or EAT cells. These data demonstrate that not only the properties of cell membrane, but also the organization of actin filaments determines the osmotic reactions of cells.