Cooperative enhancement of insulinotropic action of GLP-1 by acetylcholine uncovers paradoxical inhibitory effect of beta cell muscarinic receptor activation on adenylate cyclase activity

Miguel, J. C. , Abdel-Wahab, Y. H.A., Green, B. D., Mathias, P. C.F. and Flatt, P. R. (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. (doi: 10.1016/s0006-2952(02)01482-x) (PMID:12504804)

Abstract

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 μM) 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 Gi and/or Go 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 ρ-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), ρ-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, M1 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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Miguel, Dr Carlos
• Authors: Miguel, J. C., Abdel-Wahab, Y. H.A., Green, B. D., Mathias, P. C.F., and Flatt, P. R.
• College/School: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Dental School
• Journal Name: Biochemical Pharmacology
• Publisher: Elsevier BV
• ISSN: 0006-2952