Membrane alteration of trypsin-treated smooth muscle cells and penetration by antibodies to myosin.

Smooth muscle cells dispersed by low concentration of trypsin (0.125%) and grown in tissue culture will not bind antibodies against smooth muscle myosin added to the culture medium. These cells will attach, flatten and contract normally. When the trypsin concentration is raised to 0.25%, many of the attached cells will not flatten. Such round cells show uptake of the myosin antibody at the periphery and in the cytoplasm, using the indirect immunofluorescent technique. At a trypsin concentration of 1%, viable cells are no longer observed and all cells show uptake of myosin antibody. It is concluded from these experiments that above a crucial trypsin concentration, the membrane becomes altered sufficiently to permit the penetration of antibodies into the cell interior.