Contractility and ultrastructure of cardiac muscle of guinea pigs treated with diphtheria toxin.

The development of tension and the ultrastructure of cardiac papillary muscle of normal guinea pigs were compared to guinea pigs receiving lethal doses of diphtheria toxin. The maximal isometric force of the papillary muscles at various levels of resting tension indicated no significant difference between the control and the diphtheritic animals. Neither did the sarcomere lengths of papillary muscles, fixed at various levels of tension, show any significant difference between these two groups. Electronmicroscopy in diphtheritic animals showed intact myofilaments but marked dilatation of the T and L system as well as pathologic fat deposits adjacent to the subsarcolemma and the T system. The results, therefore, suggest that diphtheria toxin acts on the T and L system, but does not affect structure and function of the myofilaments in the acute stage of diphtheria intoxication.