Study of aging rat tail collagen using atomic force microscope.

Collagen structure of young and old rats was examined by using atomic force microscope (AFM) images. Rat tail tendons of eight and twenty-four month-old Wistar rats were digested enzymatically (pepsin), and allowed to refibrillate for 24 hours at 37 degrees C. The samples were examined using a Nanoscope III (Digital Instruments, Santa Barbara, CA, U.S.A.) with a J scanning head and a 200 microns silicon nitride cantilever. The study was performed in air and without filters. The AFM inspection of refibrillated collagen produced images showing long fibrils with relatively homogeneous heights and widths, characterized by clear banding with a periodic interval (D band) of 67 nm. With respect to collagen extracted from young rats, collagen extracted from old rats revealed fibrils exhibiting the same band interval, but with lower widths and heights. Furthermore, the depth of gap between two overlaps showed a higher mean value in the aged rats. These data are consistent with biochemical reports of collagen modifications during aging; we suggest that post-synthetic reactions might be responsible for this as they interfere with the refibrillation process and also modify the three-dimensional structure of fibrils.