Polarity in intracellular calcium signaling

The concentration of free calcium ions (Ca2+) in the cytosol is precisely regulated and can be rapidly increased in response to various types of stimuli. Since Ca2+ can be used to control different processes in the same cell, the spatial organization of cytosolic Ca2+ signals is of considerable importance. Polarized cells have advantages for Ca2+ studies since localized signals can be related to particular organelles. The pancreatic acinar cell is well-characterized with a clearly polarized structure and function. Since the discovery of the intracellular Ca2+-releasing function of inositol 1,4,5-trisphosphate (IP3) in the pancreas in the early 1980s, this cell has become a popular study object and is now one of the best-characterized with regard to Ca2+ signaling properties. Stimulation of pancreatic acinar cells with the neurotransmitter acetylcholine or the hormone cholecystokinin evokes Ca2+ signals that are either local or global, depending on the agonist concentration and the length of the stimulation period. The nature of the Ca2+ transport events across the basal and apical plasma membranes as well as the involvement of the endoplasmic reticulum (ER), the nucleus, the mitochondria, and the secretory granules in Ca2+ signal generation and termination have become much clearer in recent years.