Large scale, unbiased analysis of elementary calcium signaling events in cardiac myocytes.

The identification of spatiotemporally restricted Ca ²⁺ signals, Ca ²⁺ sparks, was instrumental for our understanding of cardiac Ca ²⁺ homeostasis. High-speed 2D confocal imaging enables acquisition of such Ca ²⁺ sparks with high-content information but their full appreciation is constrained by the lack of unbiased and easy-to-use analysis tools. We developed a software toolset for unbiased and automatic Ca ²⁺ spark analysis for huge data sets of subcellular Ca ²⁺ signals. iSpark was developed to be scanner and detector independent. In myocytes from hearts subjected to various degrees of hypertrophy we acquired >5.000.000 Ca ²⁺ sparks from 14 mice. The iSpark-enabled analysis of this large Ca ²⁺ spark data set showed that the highly organized distribution of Ca ²⁺ sparks present in healthy cells disarrayed concomitant with the development of aberrant transverse tubules and disease severity. Thus, iSpark represents a versatile and universal tool for analyzing local Ca ²⁺ signaling in healthy as well as diseased, aberrant local Ca ²⁺ signal transduction. The results from the unbiased analysis of large data sets provide a deeper insight into possible mechanisms contributing to the onset and progression of cardiac diseases such as hypertrophy.
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