Charge displacement by adhesion and spreading of a cell

The potentiostatic control of surface charge density and interfacial tensio n of an electrode immersed in an aqueous electrolyte solution offers a poss ibility for direct studies of non-specific interactions in cell adhesion. U nicellular marine alga, Dunaliella tertiolecta (Chlorophyceae) of micromete r size and flexible cell envelope was used as a model cell and 0.1 M NaCl a s supporting electrolyte. The dropping mercury electrode acted as in situ a dhesion sensor and the electrochemical technique of chronoamperometry allow ed measurement of the spread cell-electrode interface area and the distance of the closest approach of a cell. The adhesion and spreading of a single cell at the mercury electrode causes a displacement of counter-ions from th e electrical double layer over a broad range of the positive and negative s urface charge densities (from + 16.0 to - 8.2 muC/cm(2)). The flow of compe nsating current reflects the dynamics of adhesive contact formation and sub sequent spreading of a cell. The adhesion and spreading rates are enhanced by the hydrodynamic regime of electrode's growing fluid interface. The dist ance of the closest approach of an adherent cell is smaller or equal to the distance of the outer Helmholz plane within the electrical double layer, i .e. 0.3-0.5 nm. There is a clear evidence of cell rupture for the potential s of maximum attraction as the area of the contact interface exceeded up to 100 times the cross-section area of a free cell. (C) 2000 Elsevier Science S.A. All rights reserved.