Semi-automated program for analysis of local Ca2+ spark release with application for classification of heart cell type

- Local Ca2+ spark release plays a role in cardiac excitation-contraction coupling.
- We present a semi-automatic Matlab Graphical User Interface analysis program.
- The program successfully analyzes Ca2+-spark characteristics.
- We used data from sinoatrial, atrial, and ventricular cells to test the program.
- Different heart cell types are successfully classified.

Local Ca2+ spark releases are essential to the Ca2+ cycling process. Thus, they play an important role in ventricular and atrial cell contraction, as well as in sinoatrial cell automaticity. Characterizing their properties in healthy cells from different regions in the heart can reveal the basic biophysical differences among these regions. We designed a semi-automatic Matlab Graphical User Interface (called Sparkalyzer) to characterize parameters of Ca2+ spark release from any major cardiac tissue, as recorded in line-scan mode with a confocal laser-scanning microscope. We validated the algorithm on experimental images from rabbit sinoatrial, atrial, and ventricular cells loaded with Fluo-4 AM. The program characterizes general image parameters of Ca2+ transients and sparks: spark duration, which indicates for how long the spark provides Ca2+ to the closed intracellular mechanisms (typical value: 25 ± 1, 23 ± 1, 26 ± 1 ms for sinoatrial, atrial, and ventricular cells, respectively); spark amplitude, which indicates the amount of Ca2+ released by a single spark (1.6 ± 0.1, 1.6 ± 0.2, 1.4 ± 0.1 F/F0 for sinoatrial, atrial, and ventricular cells, respectively); spark length, which is the length of the Ca2+ wavelets fired out of a row of ryanodine receptors (5 ± 0.1, 5 ± 0.2, 3.4 ± 0.3 μm for sinoatrial, atrial, or ventricular cells, respectively) and number of sparks (0.14 ± 0.02, 0.025 ± 0.01, 0.02 ± 0.01 for 1 μm in 1 s for sinoatrial, atrial, and ventricular cells, respectively). This method is reliable for Ca2+ spark analysis of sinoatrial, atrial, or ventricular cells. Moreover, by examining the average value of Ca2+ spark characteristics and their scattering around the mean, atrial, ventricular and sinoatrial cells can be differentiated.

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