Repulsion and attraction by extracellular matrix protein in cell adhesion studied with nerve cells and lipid vesicles on silicon chips

The separation of membrane and substrate in cell adhesion is addressed, in particular the role of extracellular matrix proteins. Using fluorescence interference contrast microscopy, we measure a distance of 90 nm between a neuron membrane and oxidized silicon coated with laminin. For the glycocalix, we obtain 40 nm from the adhesion of neurons on polylysine. We propose that dangling laminin molecules contribute 50 nm to the total cell-solid distance by their repulsive steric force. For an unperturbed cushion of dangling laminin molecules, we estimate a thickness of 110 nm from sedimentation of giant lipid vesicles, after subtraction of membrane undulations. We propose that in cell adhesion the laminin cushion is compressed by the adhesive forces between laminin molecules and integrin receptors.