Carbamylcholine and phorbol esters desensitize muscarinic receptors by different mechanisms in rat pancreatic acini.
Pretreatment of rat pancreatic acini with phorbol 12-myristate, 13-acetate (PMA), a protein kinase C (PK-C) activator, caused the desensitization of carbamylcholine (CBC)-induced amylase release in a concentration- and time-dependent fashion. The less potent phorbol-12, 13-dibutyrate (PDBu) also provoked a desensitization, but the inactive 4-alpha-phorbol-12,13-didecanoate had no effect. PMA or PDBu also significantly reduced subsequent amylase release induced by caerulein or secretin in contrast to CBC, which only reduced amylase release induced by CBC or secretin. Preincubation of acini with PMA did not lead to a decrease in PMA or A23187-stimulated amylase release. A 3 h resting period did not restore the desensitization induced by PMA or PDBu. Pretreatment with PMA did not cause changes in muscarinic receptor high- and low-affinity populations as observed with CBC pretreatment. The PK-C inhibitor H-7 completely prevented the desensitization induced by PDBu but not that induced by CBC. TMB-8, another PK-C inhibitor, also completely prevented the desensitization induced by PDBu but only partially that induced by CBC. These results suggest that phorbol esters can induce desensitization of muscarinic receptor-stimulated amylase release by a different mechanism than that involved in muscarinic agonist-induced desensitization.
Centre de Recherche sur les Mécanismes de Sécrétion, Faculté des Sciences, Université de Sherbrooke, Québec, Canada.
L M
LM
Blanchard
B
B
Paquette
L
L
Larose
J
J
Morisset
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000681:Amylases / Q000378:metabolism*; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D010179:Pancreas / Q000378:metabolism / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects*; D012636:Secretory Rate / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007546:Isoquinolines; D010703:Phorbol Esters; D010879:Piperazines; D011976:Receptors, Muscarinic; D015240:Phorbol 12,13-Dibutyrate; D000001:Calcimycin; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D002217:Carbachol; D011493:Protein Kinase C; D000681:Amylases; D013755:Tetradecanoylphorbol Acetate