In the present study, ultrastructural changes of the smooth muscle cell s of mdx mice were clearly revealed by IVCT. It was suggested that dystrophin deficiency induced impairment of normal cell morphology, not only in the striated muscles but also in the smooth muscle cells. In dystrophic mammals, histopathological changes have been less examined in smooth muscle cells in comparison with the striated muscles [4, 5]. In the present study, smooth muscle cells with an appearance of typical necrosis or apoptosis could not be identified among thousands of examined muscle cells of the mdx mice. The reason why almost smooth muscle cells survive without normal dystrophin expression is still unknown, but there are some possibilities as follows. The elevation of the free cytosolic Ca²⁺ concentration , a potential trigger to induce cell necrosis, was revealed in the mdx skeletal muscle [13]. To the contrary, as measured with the fluorescent Ca²⁺ indicator fura-2, cytosolic Ca²⁺ concentration is not elevated in resting smooth muscle cells of mdx mice [14]. The maintenance of intracellular Ca²⁺ metabolism may contribute to keep homeostasis of the smooth muscle cells of the mdx mice [15].

In the present study, we have used our IVCT, which makes it possible to observe the morphology of dynamic cells in anesthetized animals [12]. We have already noticed that ultrastructures obtained from the specimens prepared by the conventional preparation methods contained lots of inevitable technical artifact s . In the other words, “normal” ultrastructures obtained by the standard electron microscopy are not “natural” ones. Indeed, even in the smooth muscle cell s of the normal scn mice, the conventional ultrastructural features, such as opening electron-lucent caveolae , short gap junction s , and so-called basal lamina , are definitely different from those obtained by the IVCT. The IVCT produced a very compact extracellular matrix between closely spaced smooth muscle cells in the scn mice. In contrast, dramatic changes of basement membrane s in the mdx mice were also clearly revealed by the IVCT. The extracellular matrix or basal lamina has been suggested as intramuscular microtendons that provide mechanical support during contractions of the smooth muscle layer. Although the extracellular matrix in the normal scn mice was revealed by the IVCT, showing a tighter and more compact arrangement between adjacent smooth muscle cells, the intramembrane protein dystrophin has a role to connect extracellular matrix to the cell membrane of smooth muscle cells. The extracellular matrix was easily torn off from the smooth muscle cells in the mdx mice, because of impaired molecular functions of dystrophin to maintain compact structures of smooth muscle layers. Such impairment should affect the force transmission within the extracellular matrix as “microtendons” and may decrease the substantial force of the contraction of the smooth muscle layers [9].