APVT-51-031104

Principal Investigator: Ivan Zahradník

Duration: January 2005 – December 2007
Coordinating Organization: Institute of Molecular Physiology and Genetics SAS, Bratislava

Annotation:

Excitation-contraction coupling in cardiac myocytes is mediated by calcium signalling in the tubulo-reticular junction, which includes calcium influx from the extracellular environment, calcium release from the sarcoplasmic reticulum, and inactivation of both processes. In failing heart, contractility of myocytes is impaired due to a decrease in calcium release. The aim of this proposal is to define the relationship between the organization of the tubulo-reticular junction and calcium signalling in normal and failing heart. We will employ our well-established methodological and theoretical approaches (measurement of pure calcium currents and local calcium signals, stereological analysis of the environment of organelles, modelling of reaction-diffusion processes, simulation of calcium channel activity in the tubulo-reticular junction, and geometrical modelling) that make possible to characterize the organization of the tubulo-reticular junction and calcium signalling among calcium channels.

Keywords:

myocardium, myocyte, calcium signalling, ion channels, contractility, heart failure

Objectives:

Excitation-contraction coupling in mammalian heart muscle is based on calcium signalling in the tubulo-reticular junction. Our central hypothesis is that the specific micro-architecture of the tubulo-reticular junction, consisting of juxtaposed clusters of DHPR and RyR channels, together with their specific calcium-dependent gating properties, conveys the unique properties of excitation-contraction coupling in cardiac myocytes. We particularize this hypothesis in the concept of the excitation-contraction coupling unit (ECCU). The ECCU is understood as the whole set of channels in the cardiac dyadic junction (excitation unit composed of DHPRs, and release unit composed of RyRs), defined by the conductive and gating properties, topological disposition and ionic environment of the participating channels. The objective of this proposal is to define the role of changes in the micro-architecture of cardiac muscle cells, i.e., in the properties of ECCUs as well as their cellular distribution, in compromised calcium release efficiency in the failing heart. To achieve this objective, we will extensively employ several original methods developed in our laboratories, i.e., the model of calcium current kinetics with release dependent inactivation, the software for simulation of the electrophysiological experiment based on simulation of interacting channel clusters, the technique for selective induction of calcium release-dependent inactivation of calcium current, modelling of reaction-diffusion processes in the dyad, stereological identification of the environment of organelles, and geometrical modelling of muscle cells. To identify molecular and cellular mechanisms of calcium signalling in cardiac myocytes responsible for impaired triggering of contraction in failing myocardium, we will concentrate on two closely related specific aims: (1) To test the hypothesis that the decreased efficiency and reliability of calcium-induced calcium release in heart failure is caused by changes of the ECCU; (2) To test the hypothesis that the changes in calcium release in failed myocytes are caused by changes in the disposition of ECCUs within the myocyte.

Publications: