Regulation of exocytosis via release of Ca2+ from intracellular stores

The release of Ca2+ from intracellular stores is an important trigger for s ecretion in many cell types. Depending on the spatial relationship between the intracellular Ca2+ stores and the site of exocytosis, the Ca2+ signal c an be very local or spread throughout the entire cell. Here, we review how the release of Ca2+ from inositol trisphospate (IP3)-sensitive stores contr ibutes differently to the stimulus-secretion coupling in three types of sec retory cells (acinar cells of the pancreas, gonadotrophs, and corticotrophs of the anterior pituitary gland). We propose that in both pancreatic acina r cells and pituitary gonadotrophs the IP3-sensitive stores may be in close proximity to the sites of exocytosis such that the concentration of Ca2+ a t these sites are transiently much higher than the average cytosolic Ca2+ c oncentration. In contrast, the local Ca2+ gradient is less prominent in pit uitary corticotrophs. Finally, some recent technical developments that may contribute significantly to future investigations of local Ca2+ signals are discussed. BioEssays 21:861-865, 1999. (C) 1999 John Wiley & Sons, Inc.