Cellular binding of 3H-cytochalasin B.

Abstract

AbstractThe binding of tritium‐labelled cytochalasin B (3H‐CB) to a variety of mammalian cells was investigated. Binding studies revealed near‐equilibrium binding of 3H‐CB within 5 to 10 minutes, but the equilibrium level was influenced by 3H‐CB concentration. Binding kinetics revealed strong temperature dependence. Rapid release of up to 70% of cell‐bound 3H‐CB molecules occurred when cells were washed and returned to fresh medium without CB. The remaining 30% of cell‐bound 3H‐CB molecules dissociated more slowly. Equilibrium binding studies on a variety of diploid, heteroploid and transformed cells treated with 1 μg/ml 3H‐CB revealed between 1.7 X 107 to 5.3 X 107 3H‐CB binding sites per cell. Cellular binding of 3H‐CB was not affected by inhibition of cellular energy metabolism, RNA or protein synthesis. Modification of the cell surface by proteases, neuraminidase, hyaluronidase, ribonuclease, or occupation of cell surface saccharide residues by a variety of plant lectins did not significantly alter the pattern of 3H‐CB binding. Surface pressure measurements on CB‐treated lipid monolayers indicated that CB can interact with lipid molecules. The partition of CB in hydrophobic lipid regions of cell membrane systems as a possible mechanism of cellular binding of CB is discussed. Fractionation of 3H‐CB‐treated cells revealed binding of 3H‐CB to both the plasma membrane and by intracellular membranes.