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Abstract

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.