The transverse tubular system of rat myocardium: its morphology and morphometry in the developing and adult animal.

The three dimensional arrangements of the T system in the developing and adult animal were investigated by means of high voltage electron microscope stereoscopy using Golgi treated materials. The rat myocardial T system was composed of three major group elements: the transverse tubules, longitudinal tubules and flattened cisternae, which were classified according to their orientation and to their morphological features. It was found, as the growth of the rats proceeded, that the longitudinal tubules increased in number and that the transverse tubules were arranged more regularly and densely at the level of the z band. The flattened cisternae transiently increased in number during the 2-9 weeks, and then decreased gradually. Electron microscopy also revealed that all the transverse, longitudinal tubules and flattened cisternae of the T system had the chance of forming a coupling with the sarcoplasmic reticulum irrespective of its morphology and orientation to the myofibrils. Quantitative analysis of the rat T system from the stereo images indicated that the surface area (0.299 micron2/micron3) was considerably greater than previously reported.