Mg²⁺‐dependent Ca²⁺ transport in cell membranes from the exocrine pancreas

The role of Ca2+ as an intracellular messenger for enzyme secretion in the exocrine pancreas requires its precise regulation within the cell. Using isolated pancreatic acini, it has been shown that during stimulation with secretagogues of enzyme secretion an initial phase of Ca2+ release is followed by Ca2+ reuptake. These observations have been interpreted to mean that secretagogues release Ca2+ from one or more intracellular stores (“Ca2+ trigger pool”) and also increase Ca2+ influx into the cell, which is taken up into one or more intracellular pools different from the “trigger pool.”’ Under sustained stimulation, however, regulation of the steady-state free cytosolic Ca2+ concentration requires a Ca2+-transport mechanism located in the plasma membrane that extrudes Ca2+ from the cell