Measurement of dynamic cellular and sarcomere contractile properties from the same cardiocyte

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Abstract
Previous studies have examined the dynamic properties of either sarcomere or whole myocyte contractions, but never both from the same cell. Accordingly, the present study employed computer-assisted video microscopy to examine both myocyte and sarcomere contractile function from the same cardiocyte. Cardiocytes were enzymatically isolated from the left ventricles of canine hearts, placed in a thermostatically controlled chamber and contractions were elicited by field stimulation at 1 Hz. Myocyte contractions were imaged using modulation contrast at a final magnification of 1100X and sarcomere contractions were imaged using phase contrast at a final magnification of 5500X. Using a 240 Hz high scan rate CCD camera, and a video-based edge detection system synchronized with the camera video output, the myocyte and sarcomere motion data were digitized. The digitized myocyte and sarcomere motion data was analyzed by computer to obtain contractile indices which included: the resting length, percentage shortening, and the velocity of shortening. Upon electrical stimulation, the myocytes (n=28) contracted from a resting length of 155.30±4.37/unby 3.45±0.23% and the associated velocity of shortening was 57.77±3.60/un/s. The sarcomeres from these same cells shortened from an average resting length of 1.95±0.02μm by 0.17±0.01μm and the associated velocity of shortening was 1.75±0.09μm/s. In summary, this study demonstrated that the video-based edge detection technique could be easily adapted to measure both cell and sarcomere contractile performance from the same cardiocyte.

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