CHOLECYSTOKININ REGULATES GLYCOPROTEIN MEMBRANE-COMPOSITION OF RAT PANCREATIC ZYMOGEN GRANULES

Lectin-binding studies were performed on rat pancreatic zymogen granul es to investigate the alterations in the carbohydrate membrane composi tion under both chronic CCK stimulation and long-term CCK blockade for 3, 7 and 15 days. By flow cytometry using FITC-WGA - which specifical ly binds to N-acetylglucosamine and sialic acid - we measured the amou nt of WGA molecules bound to each individual granule. Parallel studies on pancreatic secretion were also carried out. CCK treatment displaye d a differential effect on two zymogen granule subpopulations (Z(1) an d Z(2)) identified by flow cytometry on the basis of their light scatt er properties: no effects on Z(2) zymogen granules were observed in CC K-treated rats, while Z(1) granules showed a significant increase in W GA binding at day +7 which coincides with an increase in protein secre tion in response to the hormone. On the contrary, a significant decrea se in the amount of WGA receptors was observed in zymogen granule memb rane of both the Z, and Z, subsets of rats subjected to a long-term CC K blockade. Again, these changes parallel to the reduction observed in protein secretion. Our results suggest that glycoconjugates of zymoge n granule membrane involved in CCK-regulated exocytosis contain N-acet ylglucosamine and sialic acid residues whose quantities are regulated by CCK.