Twenty Years of Calcium Imaging: Cell Physiology to Dye For

Ca²⁺signal generation in the apical granular pole. The main (upper) part shows a schematic diagram of a pancreatic acinar cell with the base at the top and the apical pole at the bottom. Ca²⁺ entry is depicted from a point source (cell-attached patch pipette) at the base. Ca²⁺ entering (through capacitative Ca²⁺ entry channels; CCE) is taken up by the ER Ca²⁺ pump and diffuses in the lumen of the ER towards the apex. At the apical pole, Ca²⁺ can be released through IP₃ receptors and ryanodine channels, which can be stimulated, respectively, by IP₃ and cADPR or NAADP (acting via different intermediary receptor proteins, but both ultimately activating the ryanodine receptor). Ca²⁺ released from the ER terminals can induce further Ca²⁺ release (CICR) from the secretory (zymogen granules; ZG), assisted by IP₃ and cADPR/NAADP. The cytosolic Ca²⁺ signals are confined to the apical pole by the peri-granular mitochondrial belt. [Adapted and up-dated from (104).]