The transverse tubular system of the hypertrophic myocardium: morphology and morphometry in spontaneous hypertensive rats (SHR).

We reported previously on a modified Golgi stain that, in conjunction with high voltage electron microscope stereoscopy, gives striking views of the elaborate network of the transverse tubular system (T system) in rat myocardium. In this report we used the same techniques to study three-dimensional arrangements of the T system in the left ventricular myocardium of spontaneous hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). High voltage electron microscope stereoscopy revealed distinctive morphological characteristics of the T system, such as undulating running, short dead-end branches, and labyrinth-like tubular aggregates in the hypertrophic myocardium of SHR. Quantitative analysis of the SHR T system indicated a surface area greater than that of WKY. These findings may support the hypothesis that making an additional T system membrane will compensate for the smaller surface-to-volume ratio. However, the normal regulatory mechanism required to maintain the surface-to-volume ratio does not function properly in SHR, resulting in morphological abnormalities and functional disturbances of the myocardium.