Assaying sarcoplasmic reticulum Ca-leak in mouse atrial myocytes.

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