Atomic (scanning) force microscopy in cardiovascular research

The promise of atomic (scanning) force microscopy (AFM) for cardiovascular research is enormous. The AFM images by using a sharp cantilever tip to sense the repulsive and attractive forces between the tip and the sample surface. The force of interaction is kept constant while raster scanning, resulting in images of the surface contours with molecular and, on hard inorganic surfaces, even atomic resolution. Movement of the cantilever in the Z plane is detected by a laser beam reflected off the cantilever to a photodiode system, a piezotube allows an X and Y raster, and a three-dimensional image results. Its capabilities include: (1) the three-dimensional imaging of membranes and biomolecules with molecular and submolecular resolution; (2) such imaging not only of dry specimens but of specimens in a physiologic solution, thereby allowing the investigation of dynamic processes in both viable biomolecules and living cells; (3) the sensing of charge and intermolecular interaction forces; (4) the chemical or biochemical modification of the cantilever tip, which allows the identification of specific structures and the measurement of specific interactions (e.g., a ligand-receptor interaction); (5) nanometer control of the position and force of the cantilever, which, in turn, allows the physical manipulation of biomolecules, the dissection of biological structures (e.g., the separation of one gap junctional hemichannel from its neighbor, thereby revealing normally inaccessible surfaces), the delivery of ligands, drugs, or other materials to specific locations, and the precise measurement of interacting forces at specific sites; and (6) the modification of the apparatus by adding complementary methodologies (e.g., magnetic resonance imaging, fluorescence microscopy, confocal microscopy, and perhaps electrophysiology). AFM, however, is only now being applied to biological research, many technical and methodologic problems exist, and a number of them are considered in this review. Little work has been done in cardiovascular research, and the purpose of this review is to introduce this new and exciting approach to investigation.