Distribution of elements in the pancreatic exocrine cells determined by electron probe X-ray microanalysis

We measured the intracellular electrolytes of acinar cells by making electron probe X-ray microanalysis of hydrated and dehydrated sections of freshly frozen dog pancreas. The concentrations of electrolytes in the cytoplasm were: Na 4.8 +/- 2.1, K 132 +/- 15, Cl 14 +/- 4.7, P 165 +/- 36, S 19 +/- 2.8 and in zymogen granules: Na 6 +/- 5, K 60 +/- 16, Cl 31 +/- 20, P 36 +/- 8, S 172 +/- 25, Ca 7 +/- 5 (mean +/- S.D. mmol/kg wet weight). The cytoplasm, which is rich in rough endoplasmic reticulum, had low Na and high K concentrations, as compared with levels in the acinar cells of other exocrine glands such as the submandibular gland, the bulk of which is occupied by secretory granules. Though the representative feature of secretory granules was a high S content, occasionally low S peaks of spectra from secretory granules were obtained. These findings may reflect the content of mature zymogen granules and immature condensing vacuoles. Pilocarpine stimulation increased cytoplasmic Na, Cl and Ca and decreased K levels in the pancreatic acinar cells. This indicates that secretory stimulation increases the permeability of the cell membrane to Na, Cl and K ions and that there is a simultaneous Ca release from the intracellular Ca stores such as zymogen granules and endoplasmic reticulum, and/or Ca influx from the extracellular space.