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OBJECTIVE: The aim was to develop a novel system to measure changes in cytosolic free calcium concentration (Ca2+i) and cell motion simultaneously in a single beating myocyte by digital imaging microscopy. METHODS: Indo-1 was selected as a fluorescent calcium indicator. The particular feature of our digital imaging microscopy is that, in order to avoid cell movement artifacts, two indo-1 fluorescence images of different wavelengths are obtained at the same time at 16.7 ms intervals using two SIT cameras. Isolated ventricular myocytes were used, prepared from hearts of male Sprague-Dawley rats, weighing 350 to 400 g. RESULTS: In continuously beating cells contracted by electrical field stimulation, we can visualise changes in Ca2+i and cell shape during contraction with pseudocolour images of the fluorescence ratios, and it was found that the onset of the calcium transient preceded that of the shortening of cell length. Both isoprenaline and ouabain enhanced the magnitudes of the calcium transient and cell contraction. Furthermore, isoprenaline shortened the half decay time of the calcium transient. CONCLUSIONS: Our data suggest that the newly developed system is useful for measuring rapid changes in Ca2+i in relation to cell motion, and is particularly suitable for measuring the calcium transients in a beating cardiomyocyte.
Tamura et al. (1992) studied this question.