A concept for the physiological stiffness of a living cell

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Setting the basis for a molecular “concept of the electrical cell membrane potential” many years ago revolutionized cell research and led to an enormous progress in biosciences. Similar as the electrical cell membrane potential, cell stiffness is another fundamental physiological parameter that characterizes a living cell. At least three layers, the glycocalyx, the plasma membrane and the submembranous cytoskeleton determine the cell stiffness. We assume that the separate experimental examination of these three layers could lead to a general definition of this physiological key parameter that may be applicable to any living cell. The technical basis of this proposal forms a hybrid instrument that unifies atomic force microscopy with fluorescence microscopy. As a biological model we will use living vascular endothelial cells that are most suitable for such measurements. They have a prominent glycocalyx, a functionally well characterized plasma membrane and a dynamically active submembraneous cytoskeleton. It is planned to characterize layer by layer using various experimental methods that range from the selective removal of the glycocalyx, the expression of specific membrane proteins to varying the viscosity of the submembraneous cell layer. The project should pave the way for a first physiological concept on mechanical stiffness of living cells.