Smooth-Muscle Cells: Twist and Clout
Weisburd, Stefi, Science News
Smooth-muscle cells: Twist and clout
Researchers at the University of Vermontin Burlington may have uncorked the secret of how smooth-muscle cells contract. Physiologist David M. Warshaw and his colleagues have found evidence that, unlike skeletal muscle, which shortens like an accordion, smooth-muscle cells contract in a corkscrew-like manner. This finding, says Warshaw, could help explain why smooth muscles contract more efficiently and slowly than do skeletal muscles.
Smooth-muscle cells line holloworgans such as the stomach and bladder and are partly responsible for maintaining blood pressure in the blood vessels as well as other involuntary bodily processes. But in spite of their prevalence and obvious importance, relatively little attention has been paid to their contraction machinery, according to Warshaw. More is known about skeletal and cardiac muscles because patterns of striations, or alternating dark and light bands, on these muscle fibers have enabled scientists to study the movement and alignment of the protein strands, called myosin and actin, which do the work of contraction inside the cell.
Smooth muscles, on the other hand,are not striated and, when viewed under a microscope, do not appear to be obviously organized in any fashion that would suggest an underlying structure. Past optical microscopy had suggested that the contracting myosin and actin are arranged in helices, but this view has not been widely accepted.
In the June 12 SCIENCE, Warshaw,Whitney J. McBride and Steven S. Work offer more support for the helical camp. They electrostatically attached small resin beads to the outside of smooth-muscle cells taken from a toad's stomach. When the researchers analyzed the movement of the beads on a cell electrically stimulated to contract, they found that the cell twisted in a helix as it shortened. Moreover, as the cell relaxed and reextended, the beads rotated back in the opposite direction. …