Fibroblast‐Myocyte Interrelation in the Mammalian Heart: Experiments and Models

When considering cardiac structure and function, it is important to realize that cardiac myocytes (M), while forming bulk tissue volume, are outnumbered by non‐myocytes, chiefly fibroblasts (F). M and F show intimate spatial interrelation, with every M bordering to one or more F. Recent research revealed direct gap‐junctional coupling (by connexin 45) between F and M in rabbit sino‐atrial node [1], and highlighted the dynamic remodeling of F and M connexins in post‐ischaemic scar tissue [2]. The functional relevance of M‐F coupling is only starting to emerge [3]. In addition to the formation of ‘passive’ barriers that obstruct electrical conduction, F may potentially form: (i) current sinks [M‐(n·F)] that cause unidirectional block or delay atrio‐ventricular conduction; (ii) short‐range interconnections [M‐F‐M] that smooth propagating wavefronts in sino‐atrial node and in the cross‐sheet direction of ventricular myocardium; (iii) long‐distance communication lines [M‐(n·F)‐M] that bridge post‐transplantation or ischaemic scars. In addition, the inherent mechano‐sensitivity of F could allow them to play sensory roles relevant for cardiac mechano‐electric feedback. Supported by the UK Biotechnology and Biological Sciences Research Council and the British Heart Foundation.