Propagation and collision characteristics of calcium waves in rat myocytes

In myocytes, local contractions occur spontaneously and propagate as traveling waves. We observed the waves in myocytes as local changes in fura-2 fluorescence and determined some characteristics of the wave. Myocytes were enzymatically isolated from rat left ventricles and incubated with 2 microM fura-2/AM for 60 min. Microscopic fluorescence images of myocytes were recorded with a high-sensitivity video camera. The images were digitally analyzed, frame by frame, and temporal changes in local fluorescence were displayed. With the excitation wavelength at 380 nm, the darker band propagates as the traveling wave. With the excitation wavelength at 340 nm, the wave appears brighter. With the isosbestic wavelength at 360 nm, the wave is not discernible. The waves are thus considered to be traveling waves of change in local cytoplasmic calcium ion concentration (calcium wave). Velocity, amplitude, and width of the calcium waves appeared to be fairly constant during their propagation. When two waves propagating in opposite directions collided, summation of the waves did not occur. After the collision both waves disappeared. These observations support the idea that the waves propagate by inducing calcium release from adjacent sarcoplasmic reticulum. Phenomena observed during the collision indicate that there is a refractory period after the calcium transient; spatially, a refractory zone exists in the wake of the wave.