Sarcomere motion in isolated cardiac cells

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Abstract
Computerized image-analysis techniques have been employed to examine the sarcomere dynamics of isolated mammalian cardiac myocytes. The cells were prepared by perfusion of adult rabbit hearts with hyaluronidase-collagenase solutions; they exhibited phasic contractions in the presence of 10(-6) M Ca2+. The dissociated cells were visualized by phase microscopy and a video camera interfaced in a minicomputer. Digitized cell images were processed by an algorithm utilizing signal averaging and contrast enhancement to yield data showing individual sarcomere position and shortening vs. time, so that patterns of sarcomere activation could be observed in spontaneously contracting cells. Compared to records of whole-cell shortening and of striation displacement, computerized image analysis provided a much more faithful indication of time course and sequence of sarcomere shortening. Spontaneously contracting cells showed sequential sarcomere shortening beginning at one end and propagating longitudinally with a constant velocity, typically at 100--150 micron/s for beat rates of 40 min-1. Velocities of initial sarcomere shortening appeared to increase with elevated Ca2+. These observations are consistent with a regenerative mechanism of calcium-induced calcium release.