Examination of the Effects of Heterogeneous Organization of RyR Clusters, Myofibrils and Mitochondria on Ca2+ Release Patterns in Cardiomyocytes.
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.
Department of Mechanical Engineering, University of Melbourne, Melbourne, Australia; Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand; Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia.
Vijay
V
Rajagopal
Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia.
Gregory
G
Bass
Department of Engineering Science, University of Auckland, Auckland, New Zealand.
Cameron G
CG
Walker
Department of Physiology, University of Auckland, Auckland, New Zealand.
David J
DJ
Crossman
School of Biological Sciences, University of Auckland, Auckland. New Zealand.
Amorita
A
Petzer
School of Biological Sciences, University of Auckland, Auckland. New Zealand.
Anthony
A
Hickey
Department of Mechanical Engineering, University of Melbourne, Melbourne, Australia.
Ivo
I
Siekmann
Department of Medicine, University of California San Diego, San Diego, United States of America; National Center for Microscopy and Imaging Research, University of California San Diego, San Diego, United States of America.
Masahiko
M
Hoshijima
National Center for Microscopy and Imaging Research, University of California San Diego, San Diego, United States of America.
Mark H
MH
Ellisman
Systems Biology Laboratory, Melbourne School of Engineering, University of Melbourne, Melbourne, Australia; School of Mathematics and Statistics, Faculty of Science, University of Melbourne, Melbourne, Australia; School of Medicine, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, Australia; ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, University of Melbourne, Melbourne, Australia.
Edmund J
EJ
Crampin
Department of Physiology, University of Auckland, Auckland, New Zealand; Biomedical Physics, University of Exeter, Exeter, United Kingdom.
Christian
C
Soeller
D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D019295:Computational Biology; D003198:Computer Simulation; D008297:Male; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000378:metabolism*; D009210:Myofibrils / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000378:metabolism*
D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium