Amplitude distribution of calcium sparks in confocal images: Theory and studies with an automatic detection method

Determination of the calcium spark amplitude distribution is of critical im portance for understanding the nature of elementary calcium release events in striated muscle. In the present study we show, on general theoretical gr ounds, that calcium sparks, as observed in confocal line scan images, shoul d have a nonmodal, monotonic decreasing amplitude distribution, regardless of whether the underlying events are stereotyped. To test this prediction w e developed, implemented, and verified an automated computer algorithm for objective detection and measurement of calcium sparks in raw image data. Wh en the sensitivity and reliability of the algorithm were set appropriately, we observed highly left-skewed or monotonic decreasing amplitude distribut ions in skeletal muscle cells and cardiomyocytes, confirming the theoretica l predictions. The previously reported modal or Gaussian distributions of s parks detected by eye must therefore be the result of subjective detection bias against small amplitude events. In addition, we discuss possible situa tions when a modal distribution might be observed.