Abstract
Lectin-binding studies were performed on rat pancreatic zymogen granules to investigate the alterations in the carbohydrate membrane composition under both chronic CCK stimulation and long-term CCK blockade for 3, 7 and 15 days. By flow cytometry using FITC-WGA – which specifically binds to N-acetylglucosamine and sialic acid – we measured the amount of WGA molecules bound to each individual granule. Parallel studies on pancreatic secretion were also carried out. CCK treatment displayed a differential effect on two zymogen granule subpopulations (Z 1 and Z 2) identified by flow cytometry on the basis of their light scatter properties: no effects on Z 2 zymogen granules were observed in CCK-treated rats, while Z 1 granules showed a significant increase in WGA binding at day +7 which coincides with an increase in protein secretion in response to the hormone. On the contrary, a significant decrease in the amount of WGA receptors was observed in zymogen granule membrane of both the Z 1 and Z 2 subsets of rats subjected to a long-term CCK blockade. Again, these changes parallel to the reduction observed in protein secretion. Our results suggest that glycoconjugates of zymogen granule membrane involved in CCK-regulated exocytosis contain N-acetylglucosamine and sialic acid residues whose quantities are regulated by CCK.
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