Calcium sparks are present in trout atrial myocytes.

A The upper panel shows calcium sparks (white arrowheads) recorded in the line-scanning mode. The lower panel shows the fluorescence intensity (F/F₀) recorded in a 3 µm wide band delimited by the two red lines. B Comparison of spontaneous calcium sparks (white arrow) and a field stimulated calcium transient (black arrow). The corresponding calcium transients recorded in a 3 µm wide band delimited by the two red lines are shown in the lower panel. C Comparison of the frequency of spontaneous calcium sparks and calcium waves. The parentheses indicate the number of cells where sparks or waves were detected out of a total of 38 myocytes examined.