MEMBRANE BENDING MODULUS AND ADHESION ENERGY OF WILD-TYPE AND MUTANT-CELLS OF DICTYOSTELIUM LACKING TALIN OR CORTEXILLINS

We have employed an interferometric technique for the local measuremen t of bending modulus, membrane tension, and adhesion energy of motile cells adhering to a substrate. Wild-type and mutant cells of Dictyoste lium discoideum were incubated in a flow chamber. The flow-induced def ormation of a cell near its adhesion area was determined by quantitati ve reflection interference contrast microscopy (RICM) and analyzed in terms of the elastic boundary conditions: equilibrium of tensions and bending moments at the contact line. This technique was employed to qu antify changes caused by the lack of talin, a protein that couples the actin network to the plasma membrane, or by the lack of cortexillin I or II, two isoforms of the actin-bundling protein cortexillin. Cells lacking either cortexillin I or II exhibited reduced bending moduli of 95 and 160 k(B)T, respectively, as compared to 390 k(B)T, obtained fo r wild-type cells. No significant difference was found for the adhesio n energies of wild-type and cortexillin mutant cells. In cells lacking talin, not only a strongly reduced bending modulus of 70 k(B)T, but a lso a low adhesion energy one-fourth of that in wild-type cells was me asured.