Question: 

Subcellular myofibrils determine systolic and diastolic functions of the beating heart. The aim of this study was to investigate whether cardiac myofibrils isolated from zebrafish, a widely used model organism for studies of development, regeneration and inherited human diseases, represent a valid contractile model to study cardiac function at the sarcomeric level.

Methodology: 

Kinetic and mechanical features of these organelles isolated from adult zebrafish ventricles were analyzed in a fast kinetic mechanical setup based on an atomic force probe and video-microscopy.

Result: 

Rate constants of force development following Ca²⁺-activation (k_ACT~ 5 s^-1) and of force decay during relaxation (t_REL^-1~ 12 s^-1), isometric force at maximal (F_max~ 50 nN/mm²) or partial Ca²⁺-activations (pCa₅₀~ 5.4, n_H~ 1.7) and force responsiveness (F_pass~ 4 nN/mm²) upon an external stretch applied to the relaxed myofibril (15 % above myofibril slack length) exhibit similar values as those featuring murine cardiac myofibrils (Iorga et al., Cardiovasc Res 2008, vol.77(4)). However, electron micrographs display a relative low myofibrillar density of the adult zebrafish myocardium, similar to that found during fetal development and early postnatal period in mouse.

Conclusion: 

Despite the fact that zebrafish heart is a two-chamber organ, our results demonstrate that myofibrils isolated from this cost-effective vertebrate model organism perform similarly to those from the mouse. The present characterization lays the foundation for cellular phenotyping of zebrafish cardiac muscle in fish models of human disease.