The T-tubule system in the myocardia of the sand rat and mouse as demonstrated by horseradish peroxidase.

The transverse tubule (T-tubule) system in papillary muscles of the sand rat and the mouse were studied with the aid of a diffusion tracer (horseradish peroxidase). The T-tubule system in the sand rat showed a typical mammalian pattern with sarcolemmal tubules invaginating at the Z-band level of the sarcomere. These tubules follow a transverse direction in the cell with frequent longitudinal side-branches which connect tubules at different Z-band levels. In the mouse myocardium, the T-tubules also start as lateral invaginations from the sarcolemma at the Z-band levels. In the cell interior, however, the tubules ramify and brake up into a complicated system of spirally running tubules. These spirals, of relative small diameter (400A--700A), frequently expand and form lobulated cisternae at the Z-band levels.