The fine structure of healing over in mammalian cardiac muscle

In an effort to learn the mechanism of healing over in cardiac muscle, sheep heart false tendons containing Purkinje fibers were cut, allowed to heal over in Tyrode's solution, then fixed and examined by electron microscopy. The cut cells exhibited no evidence of a new cell membrane or any formed diffusion barrier at the cut surface and the dye ruthenium red passed freely into them. These results are incompatible with the hypothesis that healing over is due to new membrane formation at the cut surface and, therefore, support the hypothesis that healing over is the result of electrical uncoupling of the injured cells from the uninjured cells. The functional site of uncoupling could not be identified with certainty since there was no discernible change in intercellular junctions which were thought to be uncoupled. However, cells with apparent damage were observed 200 to 300 μm from the cut end, which suggests that the functional site of uncoupling may be some distance from the cut surface.