Figure 1. Schematic drawing of Ca²⁺ movement through pancreatic acinar cells.

Ca²⁺ moves from the extracellular solution (extreme right) via store‐operated CRAC channels, SERCA pumps, ER, IP₃Rs and PMCA pumps into the acinar lumen (extreme left). Diffusion of Ca²⁺ from the base of the cell to the apical pole occurs quantitatively inside the ER rather than in the cytosol because of the much higher Ca²⁺ binding capacity in the cytosol than in the ER lumen. Ca²⁺ released from the ER in the apical part of the cell via IP₃Rs activates Cl⁻ channels (ANO1) in the luminal acinar plasma membrane. ANO1, anoctamin‐1; CRAC channel, Ca²⁺ release‐activated Ca²⁺ channel; IP₃R, inositol trisphosphate receptor; PMCA, plasma membrane Ca²⁺‐activated ATPase; SERCA, sarco/endoplasmic reticulum Ca²⁺ activated ATPase.