Long-distance intercellular connectivity between cardiomyocytes and cardiofibroblasts mediated by membrane nanotubes

Aims Intercellular interactions between cardiomyocytes (CMs) and cardiofibroblasts (FBs) are important in the physiological and pathophysiological heart. Understanding such interactions is important for developing effective heart disease therapies. However, until recently, little has been known about these interactions. We aimed to investigate structural and functional connections between CMs and FBs that are distinct from gap junctions. Methods and results By membrane dye staining, we observed long, thin membrane nanotubular structures containing actin and microtubules that connected neonatal rat ventricular CMs and FBs. By single-particle tracking, we observed vehicles moving between CMs and FBs within the membrane nanotubes. By dual colour staining, confocal imaging and flow cytometry, we observed mitochondria exchange between CMs and FBs in a coculture system. By combined atomic force microscopy (AFM) and confocal microscopy, we observed calcium signal propagation from AFM-stimulated CM (or FB) to unstimulated FB (or CM) via membrane nanotubes. By membrane and cytoskeleton staining, we observed similar nanotubular structures in adult mouse heart tissue, which suggests their physiological relevance. Conclusions As a novel type of CM to FB communication, membrane nanotubes observed in vitro and in vivo provide structural and functional connectivity between CMs and FBs over long distances.