A possible site of calcium regulation in rat exocrine pancreas cells: an X-ray microanalytical study

We analysed four subcellular compartments in rat exocrine pancreas cells, zymogen granules, cytoplasm surrounding the zymogen granules, mitochondria and cytoplasm in the basal part of the cells for sodium, magnesium, phosphorus, sulfur, chlorine, potassium and calcium content, using ultrathin frozen-dried cryosections. The highest concentrations of calcium were measured in the zymogen granules and the surrounding apical part of the cell containing Golgi apparatus, smooth endoplasmic reticulum and condensing vacuoles. Calcium concentrations in the basal part of the cells (mostly rough endoplasmic reticulum) were 60% lower than in the apical part of the cells. The lowest calcium concentrations were measured in mitochondria. The results suggest that other subcellular compartments than the rough endoplasmic reticulum and mitochondria might be involved in the intracellular Ca2+ regulation.