The anatomical location of the series elastic component in rat vascular smooth muscle.

1. Flash photomicrographs using Nomarski optics have been taken of the smooth muscle cells in an activated arterial resistance vessel preparation (i.d. approximately 150 micrometers) before and after a quick release of internal circumference in an attempt to determine the location of the series elastic component (s.e.c.). 2. If the s.e.c. lies mainly within the smooth muscle cells, then, while the position of an intracellular structure would change during a release, there would be little change in its position after the release during tension recovery. 3. The movement of intracellular structures during a quick release, x, and the corresponding movement during tension recovery, y, was determined by taking double flash exposures at the appropriate times and measuring the separation of the double images on the film. In eighty-five pairs of measurements from seven vessels the ratio y/x was equal to 0.21 +/- 0.02 (S.E.). 4. The results show that less than half of the smooth muscle s.e.c. resides in extracellular components. The active dynamic stiffness of smooth muscle cells is substantially less than that of skeletal muscle fibres.