Calcium waves in mammalian heart: quantification of origin, magnitude, waveform, and velocity

A dual, digital, indo‐1 fluorescence imaging system was used to obtain high‐speed ratiometric images of [Ca 2+ ] i waves in single voltage‐clamped mammalian cardiac cells. The spatiotemporal origin of [Ca 2+ ] i waves in depolarized cells was detected as the spontaneous appearance, over 100‐300 ms, of domelike regions of elevated [Ca 2+ ] i , approximately 20 μm in diameter and 300 nM at the center. Images of [Ca 2+ ] i taken at 67‐ms intervals during propagation of [Ca 2+ ] i waves revealed that the [Ca 2+ ] i wave front was 1 ) constant in shape, 2 ) spatially steep, typically rising from 500 to 1200 nM in about 10 μm, and 3 ) propagating at constant velocity, typically 100 μm/s at 22°C. The observed spatial and temporal patterns of origin and propagation of [Ca 2+ ] i waves are consistent with the hypothesis that [Ca 2+ ] i waves arise from propagating Ca 2+ ‐induced release of Ca 2+ mediated by diffusion of cytosolic Ca 2+ . The [Ca 2+ ] i waves are smaller in peak magnitude and can occupy a larger fraction of the cell than thought previously on the basis of indirect observations.— T akamatsu , T.; W ier , W. G. Calcium waves in mammalian heart: quantification of origin, magnitude, waveform, and velocity. FASEB J. 4: 1519‐1525; 1990.