Figure 2.

Ultrastructural characteristics of interstitial structures in atrial biopsy samples. (A) Light microscopy image of atrial tissue with mild fibrosis and increased interstitial space. Masson’s trichrome staining. (B) Transmission electron microscopy showed that the intercellular space, which was considered as structureless by light microscopy, was filled with plasma components (*) and interspersed with immature collagen fibrils (c). (C) Collagen fibrils extended toward the intercellular space from the surface of pseudopodia-like projections (p) of fibroblasts. (D) Laminarization of the capillary basement membrane (double arrow) was observed, indicating increased vascular permeability. The electron densities of intracapillary plasma components and interstitial plasma components were consistent (*). (E) Light microscopy image of atrial tissue with severe intercellular fibrosis. (F) Transmission electron microscopy image of (E). The intercellular area was filled with tight collagen fibrils. Scale bars = 2 μm in (B and C), 1 μm in (D), and 5 μm in (F). Cap, capillary; CM, cardiomyocyte; N-FB, nucleus of fibroblast; FB, fibroblast.