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

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Abstract
The role of Ca2+ in stimulus-secretion coupling was analyzed in the isolated and perfused rat pancreas. The omission of [Ca2+]0 [Ca2+ concentration of perfusion medium] diminished but did not abolish the release of amylase in response to continuous stimulation with 5 m units 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+]0 was reestablished. The addition of Mn2+ (1.0 mM) to the extracellular environment containing 2.5 mM-Ca2+ reversibly inhibited the Pz-induced release of amylase. 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. The Ca2+ influx into the acinar cells is the major contributor to the rise in [Ca2+]i [intracellular Ca2+ concentration] which, in turn, mediates the processes in the stimulus-secretion coupling in the exocrine pancreas, and suggests that the mode of Ca influx is a facilitated diffusion.