Mechanical inhomogeneity of myocardium studied in parallel and serial cardiac muscle duplexes: experiments and models

We investigate, both experimentally and theoretically, contribution of the myocardium mechanical inhomogeneity to the contractile function. We developed three approaches, named as Muscle Duplex Methods, to study the specific effects and mechanisms of interaction in the simplest myocardial system consisting of two muscular units connected either in parallel or in series. Our experimental approach is designed to study the interaction between two isolated mechanically inhomogeneous cardiac muscles. The virtual duplex approach is based on a mathematical model of the myocardium contraction. The hybrid duplex approach has been designed to support, in real time, interaction between a natural muscle and its virtual counterpart. Using these approaches we showed the existence of a fine alignment between mechanical characteristics of interacting inhomogeneous myocardial elements. Contractile properties of the elements together with particular sequences and time delays in their stimulation specifically determine this alignment. We term as “tuning effects” all the phenomena concerning the interaction between inhomogeneous systemʹs elements. Within the framework of the mathematical model we showed that the key mechanism underlying tuning effects is a feedback between mechanical conditions and cooperative Ca2+ binding by troponin C. Thanks to the model analysis, we also hypothesize that mechanical inhomogeneity of myocardium is apt to produce its electrical inhomogeneity.