More and more studies have suggested an essential role of sarcoplasmic reticulum (SR) Ca2+ leak of atrial myocytes in atrial diseases such as atrial fibrillation (AF). The increasing interest in atrial Ca2+ signaling makes it necessary to develop a more accurate approach for Ca2+ measurement in atrial myocytes due to obvious differences between atrial and ventricular Ca2+ handling. In the present study, we proposed a new approach for quantifying total SR Ca2+ leak in atrial myocytes with confocal line-scan Ca2+ images. With a very precious approximation of the histogram of normalized line-scan Ca2+ images by using a modified Gaussian distribution, we separated the signal pixel components from noisy pixels and extracted two new dimensionless parameters, Fsignals and Rsignals, to reflect the summation of signal pixels and their release components, respectively. In the presence of tetracaine blocking SR Ca2+ leak, the two parameters were very close to 0, and in atrial myocytes under normal conditions, the two parameters are well positive correlative with Ca2+ spark frequency and total signal mass, the two classic readouts for SR Ca2+ leak. Consistent with Ca2+ Spark readouts, the two parameters quantified a significant increase of SR Ca2+ leak in atrial myocytes from mice harboring a leaky type 2 ryanodine receptor mutation (RyR2-R2474S+/−) compared to the WT group. Collectively, this study proposed a simple and effective approach to quantify SR Ca2+ leak in atrial myocytes, which may benefit research on calcium signaling in atrial physiology and diseases.
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