Abstract
1. The influence of Ca and Sr on the electrical coupling of canine Purkinje cells was investigated by injecting the ions electrophoretically into the cytoplasm. 2. It was found that the intracellular injection produced electrical uncoupling which was spontaneously reversed. 3. No change in resting potential of the cell adjacent to the injection site was found except in those fibres not completely healed. 4. The input resistance of the injected cell increased concomitantly with the establishment of the electrical uncoupling. 5. Caffeine (6mM), added to the extracellular fluid, reduced the rate of spontaneous recoupling. Reduction of temperature of the Tyrode solution had the same effect. 6. The abolition of cell communication produced by Ca injection seems to indicate that the ion plays an important role in the control of junctional conductance in heart fibres.