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Intercellular Ca2+ waves in rat heart muscle

1 Confocal laser scanning microscopy was used to visualize intercellular transmission of Ca2+ waves in intact rat ventricular trabeculae micro‐injected with the calcium indicator fluo‐3. 2 Ca2+ waves usually failed to be transmitted from cell to cell. At identified individual end‐to‐end cell contacts, successful transmission interspersed with failure, which sometimes occurred despite an apparent small spritz of Ca2+ between cells. The probability of cell to cell transmission (Ptran) was 0.13. 3 Ca2+ waves arose preferentially near junctions of connected cells, where connexin‐43 was found, but randomly in enzymatically disconnected heart cells. 4 β‐Adrenergic stimulation significantly increased Ptran (to 0.22) and heptanol, an uncoupler of gap junction channels, significantly decreased it (to 0.045). 5 In regions of high [Ca2+]i due to damage, wave frequency decreased markedly with each cell‐cell junction passed. 6 The Ca2+ permeability of cardiac gap junctions may be regulated, and the low ability of cardiac gap junctions to transmit Ca2+ may help control the spread of Ca2+ from damaged regions.