The bulbus arteriosus of goldfish, Carassius auratus, possesses unique structural features.
The wall of the bulbus arteriosus is exceptionally thick, with an inner surface characterized by
longitudinally arranged finger-like ridges, resulting in an uneven luminal appearance. These ridges
are covered by endocardium and encased in an amorphous extracellular matrix. The inner surface
of the bulbus arteriosus also contains rodlet cells at different developmental stages, often clustered
beneath the endothelium lining the bulbar lumen. Ruptured rodlet cells release their contents via
a holocrine secretion process. The high abundance of rodlet cells in the bulbus arteriosus suggests
that this is the site of origin for these cells. Within the middle layer of the bulbus arteriosus, smooth
muscle cells, branched telocytes (TCs), and collagen bundles coexist. TCs and their telopodes form
complex connections within a dense collagen matrix, extending to rodlet cells and macrophages.
Moreover, the endothelium makes direct contact with telopodes. The endocardial cells within the
bulbus arteriosus display irregular, stellate shapes and numerous cell processes that establish direct
contact with TCs. TEM reveals that they contain moderately dense bodies and membrane-bound
vacuoles, suggesting a secretory activity. TCs exhibit robust secretory activity, evident from their
telopodes containing numerous secretory vesicles. Furthermore, TCs release excretory vesicles
containing bioactive molecules into the extracellular matrix, which strengthens evidence for telocytes
as promising candidates for cellular therapies and regeneration in various heart pathologies.