Twenty Years of Calcium Imaging: Cell Physiology to Dye For

Calcium sparks and transverse tubules (TTs). The Ca²⁺ indicator fluo-3 was loaded into heart cells to enable Ca²⁺ sparks to be visualized on a confocal microscope. A. Signal-averaged Ca²⁺ sparks. B. Sulforhodamine B was added to the extracellular solution to image the TTs, and Ca²⁺ sparks were imaged simultaneously. C. A surface plot shows the relationship between signal-averaged Ca²⁺ sparks (A) and TTs (B). The site of the origin of the majority of Ca²⁺ sparks is the TT from the junctional SR (jSR). [See (29).]