Fig. 4. Organization of the contractile cytoskeleton in transfected cardiomyocytes. The transfected cardiomyocytes can be grouped into four classes based on the degree of organization of the contractile cytoskeleton. Non-striated cells contain brightly fluorescent myofilaments but lack the organized repeating units characteristic of myofibrils. Striated-1 cells contain a mixture of non-striated myofilaments interspersed with thin and misaligned striated myofibrils. Striated-2 cells contain predominantly striated myofibrils; however, this class lacks lateral alignment of the myofibrils. Striated-3 cells are packed with laterally aligned striated myofibrils that stretch between cell attachment points. The magnification is the same in all four panels.