Viewing the renal epithelium with the atomic force microscope.

The atomic force microscope (AFM) was invented in 1986. It created the possibility to study the surfaces of biological material at the molecular level. The AFM is not only a microscope with atomic resolution (at least when applied to suitable samples) but is also an instrument with a broad variety of other applications. We present five examples demonstating the application of the AFM technique in different ways, mainly in renal epithelium. First, it was used as a high-resolution near-field microscope which generated images of canine kidney chromosomes. Second, dynamic changes of the plasma membrane of canine kidney cells were visualized with a resolution at least 10-fold greater than that obtainable by light microscopy. Third, the AFM was used as a tool which interacted directly with the plasma membrane of canine kidney cells. Fourth, due to its excellent resolution in the third dimension (namely height), continuous measurements of changes in 'height' of multimers of cloned plasma membrane potassium channel proteins of rat kidney (ROMK1) in response to ATP were performed with a time resolution of about 100 ms in physiological buffer. Fifth, the AFM continuously followed dissociation processes of multimeric macromolecules (such as transcription factors) under physiological conditions and, on the basis of individual molecular volume measurements, allowed estimation of the number of monomers in a multimeric complex. Taken together, the AFM offers a wide spectrum of novel approaches for the experimental nephrologist.