Spontaneous calcium waves without contraction in cardiac myocytes.

Spontaneous Ca2+ waves were visualized in quiescent cardiomyocytes loaded with the Ca(2+)-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 microns/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.