Myocardial sarcomeres spontaneously oscillate with the period of heartbeat under physiological conditions

During heartbeat, the repeated contractions of myocardium are induced by the oscillation of intracellular Ca2+ concentration. On the other hand, when intermediately activated at a certain Ca2+ concentration, cardiac myofibrils exhibit the spontaneous sarcomeric oscillation (Ca-SPOC) under steady ionic conditions. In the present study, we found that Ca-SPOC occurred over a wide range of Ca2+ concentrations, including physiological contractile conditions, in skinned myocardium prepared from various animal species (rat, rabbit, pig, and cow). The period of sarcomeric oscillation fell within the same range as the period of heartbeat of each animal species. On the basis of these results we propose that the intrinsic auto-oscillatory property of sarcomeres (myofibrils) significantly contributes to myocardial beating in vivo.