Cholecystokinin regulates glycoprotein membrane composition of rat pancreatic zymogen granules.
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 (Z1 and Z2) identified by flow cytometry on the basis of their light scatter properties: no effects on Z2 zymogen granules were observed in CCK-treated rats, while Z1 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 Z1 and Z2 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.
de Dios
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Department of Physiology and Pharmacology, Campus Miguel de Unamuno, University of Salamanca, Spain. bel@gugu.usal.es
Rodriguez
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García-Montero
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Orfao
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Manso
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D000818:Animals; D001570:Benzodiazepinones / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology*; D003594:Cytoplasmic Granules / Q000187:drug effects* / Q000378:metabolism; D020109:Devazepide; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives; D058851:GPI-Linked Proteins; D007425:Intracellular Membranes / Q000187:drug effects; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D010189:Pancreatic Juice / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D014909:Wheat Germ Agglutinins
D001570:Benzodiazepinones; D058851:GPI-Linked Proteins; C066161:Gp2 protein, rat; D008562:Membrane Glycoproteins; D014909:Wheat Germ Agglutinins; C047939:fluorescein isothiocyanate-wheat germ agglutinin; D002766:Cholecystokinin; D016650:Fluorescein-5-isothiocyanate; D020109:Devazepide