Miguel, JC, Abdel-Wahab, Yasser, Green, BD, Mathias, PCF and Flatt, Peter (2003) Cooperative enhancement of insulinotropic action of GLP-1 by acetylcholine uncovers paradoxical inhibitory effect of beta cell muscarinic receptor activation on adenylate cyclase activity. BIOCHEMICAL PHARMACOLOGY, 65 (2). pp. 283-292. [Journal article]
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The cooperative effect of glucagon-like peptide 1 (GLP-1) and acetylcholine (ACh) was evaluated in a beta cell line model (BRIN BD11). GLP-1 (20 nM) and ACh (100 muM) increased insulin secretion by 24-47%, whereas in combination there was a further 89% enhancement of insulin release. Overnight culture with 100 ng/mL pertussis toxin (PTX) or 10 nM PMA significantly reduced the combined insulinotropic action (P < 0.05 and P < 0.001, respectively) and the sole stimulatory effects of GLP-1 (PTX treatment; P< 0.01) or ACh (PMA treatment; P < 0.05). Under control conditions, ACh (50 nM-1 mM) concentration-dependently inhibited by up to 40% (P < 0.001) the 10-fold (P < 0.001) elevation of cyclic 3',5'-adenosine monophosphate (cAMP) induced by 20 nM GLP-1. The paradoxical inhibitory action of ACh was abolished by PTX pre-treatment, suggesting involvement of G(i) and/or G(o) G protein alpha subunit. Effects of selective muscarinic receptor antagonists on the concentration-dependent insulinotropic actions of ACh (50 nM-1 mM) on 20 nM GLP-1 induced insulin secretion revealed inhibition by rho-FHHSiD (M3 antagonist, P < 0.05), stimulation with pirenzepine (M1 antagonist, P < 0.001) and no significant effects of either methoctramine (M2 antagonist) or MT-3 (M4 antagonist). Antagonism of M2, M3 and M4 muscarinic receptor effects with methoctramine (3-100 nM), rho-FHHSiD (3-30 nM) or MT-3 (10-300 nM) did not significantly affect the inhibitory action of ACh on GLP-1 stimulated cAMP production. In contrast, M I receptor antagonism with pirenzepine (3-300 nM) resulted in a concentration-dependent decrease in the inhibitory action of ACh on GLP-1 stimulated cAMP production (P < 0.001). These data indicate an important functional cooperation between the cholinergic neurotransmitter ACh and the incretin hormone GLP-1 on insulin secretion mediated through the M3 muscarinic receptor subtype. However, the insulinotropic action of ACh was associated with a paradoxical inhibitory effect on GLP-1 stimulated cAMP production, achieved through a novel PTX- and pirenzepine-sensitive M1 muscarinic receptor activated pathway. An imbalance between these pathways may contribute to dysfunctional insulin secretion. (C) 2002 Elsevier Science Inc. All rights reserved.
|Item Type:||Journal article|
|Faculties and Schools:||Faculty of Life and Health Sciences|
Faculty of Life and Health Sciences > School of Biomedical Sciences
|Deposited By:||Professor Peter Flatt|
|Deposited On:||14 Dec 2009 16:28|
|Last Modified:||14 Dec 2009 16:28|
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