Do calcium waves propagate between cells and synchronize alternating calcium release in rat ventricular myocytes?

The aim was to investigate the propagation of Ca(2+) waves between cells and determine whether this synchronizes alternating Ca(2+) release between cells. Experiments were carried out on electrically coupled cell pairs; spontaneous Ca(2+) waves were produced by elevating external Ca(2+). There was a significant difference in the ability of these waves to propagate between cells depending on the orientation of the pairs. Although almost all pairs connected by side-to-side contacts showed propagating Ca(2+) release, this was very uncommon in end-to-end cell pairs. Confocal studies showed that there was a gap at the intercalated disc consisting of cell membranes and a region of cytoplasm devoid of sarcoplasmic reticulum. This gap was 2.3 μm in length and is suggested to interfere with Ca(2+) wave propagation. The gap measured was much smaller between side-to-side contacts: 1.5 μm and so much less likely to interfere with propagation. Subsequent experiments investigated the synchronization between cells of Ca(2+) alternans produced by small depolarizing pulses. Although this alternation results from beat-to-beat alternation of intracellular Ca(2+) wave propagation, there was no evidence that propagation of Ca(2+) waves between cells contributed to synchronization of this alternans.