Spontaneous Calcium Waves without Contraction in Cardiac Myocytes

Spontaneous Ca²⁺ waves were visualized in quiescent cardiomyocytes loaded with the Ca²⁺-sensitive fluorescent probe, Fluo-3, and imaged by laser confocal microscopy. No sarcomere shortening was detected during wave propagation. This type of Ca²⁺ waves began at the periphery or in a central region of a myocyte and propagated the length of the cell in one or two directions. The average velocity of wave propagation was 32 μm/sec and the estimated concentration of Ca²⁺ oscillated from 124, at the bottom, to 311 nM, at the pick of the wave. Ca²⁺ waves were not confined to a single cell but could spread from cell to cell. These results describe a type of spontaneous Ca2⁺ waves which does not induce a contractile response in cardiomyocytes.