Acetylcholine-induced zymogen granule exocytosis: comparison between acini and single pancreatic acinar cells

Numerous studies have been carried out on the agonist-evoked calcium responses of single pancreatic acinar cells; however, several reports have shown that dissociation of the exocrine pancreas into predominantly single cells has an adverse effect on agonist-evoked amylase secretion.

To determine whether single acinar cells behave in an anomalous manner compared with cells within an intact acinus, we measured exocytosis in both single acinar cells and acini (2-5 cells) present in the same preparation. Exocytosis of individual zymogen granules was quantified in real-time by using the technique of continuous time-differential analysis of brightfield digital images.

Basal rates of exocytosis were low in both single cells and intact acini. Application of 10 microM acetylcholine for 6 minutes stimulated a biphasic secretory response in acinar cells. Additionally, we found that exocytotic events occur repetitively in specific locations within the apical domain; i.e., there are exocytotic "hot spots." There were no statistically significant differences between the exocytotic rates, nor were there any differences in the characteristics of the exocytotic hot spots of single cells compared with those of acini.

We conclude that time-differential analysis of brightfield images appears to be a useful tool for the investigation of the role of gap junctions in zymogen granule exocytosis and that single acinar cells provide a reasonable model for studies of acinar cell signaling and secretion.