Cellular geography of IP3 receptors, STIM and Orai: a lesson from secretory epithelial cells.

Pancreatic acinar cells exhibit a remarkable polarization of Ca2+ release and Ca2+ influx mechanisms. In the present brief review, we discuss the localization of channels responsible for Ca2+ release [mainly IP3 (inositol 1,4,5-trisphosphate) receptors] and proteins responsible for SOCE (store-operated Ca2+ entry). We also place these Ca2+-transporting mechanisms on the map of cellular organelles in pancreatic acinar cells, and discuss the physiological implications of the cellular geography of Ca2+ signalling. Finally, we highlight some unresolved questions stemming from recent observations of co-localization and co-immunoprecipitation of IP3 receptors with Orai channels in the apical (secretory) region of pancreatic acinar cells.