Examination of the Effects of Heterogeneous Organization of RyR Clusters, Myofibrils and Mitochondria on Ca² Release Patterns in Cardiomyocytes.

Rajagopal, Vijay; Bass, Gregory; Walker, Cameron G.; Crossman, David J.; Petzer, Amorita; Hickey, Anthony; Siekmann, Ivo; Hoshijima, Masahiko; Ellisman, Mark H.; Crampin, Edmund J.; Soeller, Christian

Spatio-temporal dynamics of intracellular calcium, [Ca2 ]i, regulate the contractile function of cardiac muscle cells. Measuring [Ca2 ]i flux is central to the study of mechanisms that underlie both normal cardiac function and calcium-dependent etiologies in heart disease. However, current imaging techniques are limited in the spatial resolution to which changes in [Ca2 ]i can be detected. Using spatial point process statistics techniques we developed a novel method to simulate the spatial distribution of RyR clusters, which act as the major mediators of contractile Ca2 release, upon a physiologically-realistic cellular landscape composed of tightly-packed mitochondria and myofibrils. We applied this method to computationally combine confocal-scale (~ 200 nm) data of RyR clusters with 3D electron microscopy data (~ 30 nm) of myofibrils and mitochondria, both collected from adult rat left ventricular myocytes. Using this hybrid-scale spatial model, we simulated reaction-diffusion of [Ca2 ]i during the rising phase of the transient (first 30 ms after initiation). At 30 ms, the average peak of the simulated [Ca2 ]i transient and of the simulated fluorescence intensity signal, F/F0, reached values similar to that found in the literature ([Ca2 ]i ≈1 μM; F/F0≈5.5). However, our model predicted the variation in [Ca2 ]i to be between 0.3 and 12.7 μM (~3 to 100 fold from resting value of 0.1 μM) and the corresponding F/F0 signal ranging from 3 to 9.5. We demonstrate in this study that: (i) heterogeneities in the [Ca2 ]i transient are due not only to heterogeneous distribution and clustering of mitochondria; (ii) but also to heterogeneous local densities of RyR clusters. Further, we show that: (iii) these structure-induced heterogeneities in [Ca2 ]i can appear in line scan data. Finally, using our unique method for generating RyR cluster distributions, we demonstrate the robustness in the [Ca2 ]i transient to differences in RyR cluster distributions measured between rat and human cardiomyocytes.

HEART cells; MYOFIBRILS; MITOCHONDRIA; CALCIUM channels; ELECTRON microscopes

PLoS Computational Biology, 2015, Vol 11, Issue 9, p1

1553-734X

Academic Journal

10.1371/journal.pcbi.1004417