Stimulus‐secretion coupling in pancreatic acinar cells: inhibitory effects of calcium removal and manganese addition on pancreozymin‐induced amylase release.

The role of Ca ions in stimulus‐secretion coupling has been analysed in the isolated and perfused rat pancreas. 2. The omission of [Ca2+]O diminished but did not abolish the release of amylase in response to continuous stimulation with 5 m‐u. pancreozymin (Pz)/ml. The addition of Mn2+ (1‐0 mM) to this Ca‐deficient environment abolished the residual release of amylase. This was followed by a complete recovery of amylase output when the control [Ca2+]O was reestablished. 3. The addition of Mn2+ (1‐0 mM) to the extracellular environment containing 2‐5 mM‐Ca2+ reversibly inhibited the Pz‐induced release of amylase. 4. A kinetic scheme based on competition of Ca and Mn at a carrier in the acinar cell membrane could quantitatively explain the effects of Ca and Mn upon the Pz‐induced amylase release. 5. These results support the view that the Ca2+ influx into the acinar cells is the major contributor to the rise in [Ca2+]i which, in turn, mediates the processes in the stimulus‐secretion coupling in the exocrine pancreas, and suggest that the mode of Ca influx is a facilitated diffusion.