Observations on the fine structure of nodal, Purkinje and working myocardial cells isolated from rabbit hearts.

Sinoatrial and atrioventricular nodal cells as well as Purkinje and working myocardial cells isolated enzymatically from rabbit hearts were examined by transmission electron microscopy. The cardiac cell fine structure remained well organized in the storage solution after isolation. In normal Tyrode solution, the nodal cells changed from spindle shaped to spherical, whereas the shapes of Purkinje and working myocardial cells remained unchanged. The nodal cell fine structure became disorganized with respect to its sarcomeric arrangement in normal Tyrode solution. This was assumed to result from a combination of several factors seen in the nodal cells: the loss of the normal anchoring of the myofibrils at the previous intercalated discs, breakdown of the Z bands and the alteration of the integrity of the intermediate filaments. Also, extensive restoration of plasma membrane damaged by of the intermediate filaments. Also, extensive restoration of plasma membrane damaged by the isolation procedure was observed in this solution. This might correspond to the retention of the normal physiological properties of the plasma membrane of the nodal cells despite gross morphological changes undergone in normal Tyrode solution.