Fig. (2). Initiation and propagation of cytosolic calcium increases in acinar cells.

Release of calcium via apically localized IP₃Rs triggers the initial apical rise in cytosolic [Ca²⁺] following cell stimulation. The calcium signal is then propagated towards the basal region of the cell. It is suggested that apically localized channels are activated first followed by those in the lateral and basal regions of the cell. Activation of calcium entry channels allows a sustained rise in cytosolic [Ca²⁺] which is required to drive fluid secretion.