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

Abstract

A dual, digital, indo-1 fluorescence imaging system was used to obtain high-speed ratiometric images of [Ca²⁺]_i waves in single voltage-clamped mammalian cardiac cells. The spatiotemporal origin of [Ca²⁺]_i waves in depolarized cells was detected as the spontaneous appearance, over 100-300 ms, of domelike regions of elevated [Ca²⁺]_i, approximately 20 μm in diameter and 300 nM at the center. Images of [Ca²⁺]_i taken at 67-ms intervals during propagation of [Ca²⁺]_i waves revealed that the [Ca²⁺]_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 [Ca²⁺]_i waves are consistent with the hypothesis that [Ca²⁺]_i waves arise from propagating Ca²⁺-induced release of Ca²⁺ mediated by diffusion of cytosolic Ca²⁺. The [Ca²⁺]_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.— Takamatsu, T.; Wier, W. G. Calcium waves in mammalian heart: quantification of origin, magnitude, waveform, and velocity. FASEB J. 4: 1519-1525; 1990.