Ultrastructure of telocytes, a new type of interstitial cells in the myocardium of the Chinese giant salamander (Andrias davidianus)

Abstract

Telocytes (TCs) are new interstitial cells, and they are involved in tissue regeneration, particularly in heart. Therefore, TCs are suggested to be a promising cell in regenerative medicine. However, the information of location structural characteristics and functions of TCs is still limited. In this study, cardiac TCs of the Chinese giant salamanders (Andrias davidianus) were identified by transmission electron microscopy. TCs were located in the interstitium between cardiomyocytes (CM). TCs possessed distinctive ultrastructural characteristics, including one to two very long and thin moniliform telopodes (Tps), emerging points from the cell body, caveolae, dichotomous branchings, labyrinthic systems, neighbouring exosomes and homo-cellular contacts between Tps. TCs/Tps were frequently observed in close proximity to cardiomyocytes. Moreover, Tps established hetero-cellular contacts with cardiomyocytes. Our results confirm the presence of TCs in the myocardium of the A. davidianus. This will help us to better understand roles of TCs in amphibian hearts.

Figure 1.

Light microphotographs of the myocardium of the A. davidianus. A,B) H&E staining. C,D) Toluidine blue staining. Telocytes (TC) with long and thin telopodes (Tp; black arrows) are located between cardiomyocytes (CM), and TCs also surround cardiomyocytes (CM).

Figure 2.

TEM micrographs of the myocardium of the A. davidianus. A,B) Two telocytes (TC) with long and thin telopodes (Tp; black arrows) including short branchings (yellow arrowheads,) are observed between cardiomyocytes (CM); TCs and their Tps are found close to CM; the homo-cellular close contacts (blue arrow) are established between Tps. C) Sinuous Tps form labyrinthic systems.

Figure 3.

TEM micrographs of the myocardium of the A. davidianus. A) Two telopods (Tp1 and Tp2) are observed in close proximity to cardiomyocyte (CM), which contains mitochondria (m) and myofibrils (mf); abundant caveolae (arrowheads) are located near myofibrils. Tp consist of thin podomers and thick podoms. The podoms contain mitochondria and caveolae. B) Tp surrounds a CM; a close contact (red arrow) between Tp4 and CM is observed; black thin arrows note a continuous basal lamina; red outline notes desmosome. coll, collagen fibers.

Figure 4.

TEM micrographs of the myocardium of the A. davidianus. A) Two telopods (Tp3 and Tp4, black thick arrows) form a nonclosed ring and surround two cardiomyocytes (CM1 and CM2); the closed Tp2 surrounds a cardiomyocyte (CM3); the Tp1 contains podoms and podomers, and its segments form a closed loop; two exosomes (white dashed line boxed area) are found in close proximity to the Tp1 loop. B) High-magnification TEM micrograph of the black dashed line boxed areas shown in (A) with details of Tps segment containing a non-continuous basal lamina (black thin arrows). C) High-magnification TEM micrograph of the white dashed line boxed areas shown in (A) with details of the exosomes. D) High-magnification TEM micrograph of the red dashed line boxed areas shown in (A) with details of the Tp segments, which contains thick podom and thin podomer.

Figure 5.

TEM micrographs of the myocardium of the A. davidianus. A) Four telopods (Tp1-4, black arrows) are observed in vicinity of a cardiomyocyte (CM); the dashed line boxed areas show the close contacts between Tps, Tps and CM. B) High-magnification TEM micrograph of the red dashed line boxed areas shown in (A) with the details of hetero-cellular close contacts (red arrow) between Tp1 and CM. C,D) High magnification TEM micrograph of the white and black dashed line boxed areas shown in (A) with details of homocellular close contacts (blue arrows) between Tps, respectively. mf, myofibrils; m, mitochondrion; coll, collagen fibers; black arrowheads, caveolae.

Figure 6.

A schematic diagram of structural relationships between telocytes (TC) and cardiomyocytes (CM) in the myocardium of A. davidianus. Tp, telopode.