Detection of surface movements on single smooth muscle cells: digital video microscopy.

The shortening response of isolated single smooth muscle cells from the toad stomach "Bufo marinus", was studied using digital video microscopy. A computer program was developed to rapidly on-line digitize and store successive video images of the cell as it shortened. Single smooth muscle cells were decorated with tiny anionic exchange resin beads which served as markers for surface motion. Through an interactive software routine, the cell's outline and bead images were defined. Given this information, the program determined the beads location along the length of the cell as well as its angular position on the cell surface. The program allowed the investigator to reconstruct three dimensional images of the cell during contraction. Analysis of successive cell images revealed that during cell shortening, beads would rotate on the cell surface. These data were interpreted as evidence for corkscrew-like shortening in single smooth muscle cells.