Cholinergic Stimulation of Amylase Secretion from Pancreatic Acinar Cells Studied with Muscarinic Acetylcholine Receptor Mutant Mice

Abstract

Muscarinic acetylcholine receptors (mAChRs) expressed by pancreatic acinar cells play an important role in mediating acetylcholine-dependent stimulation of digestive enzyme secretion. To examine the potential roles of M 1 and M 3 mAChRs in this activity, we used M 1 and M 3 receptor single knockout (KO) and M 1 /M 3 receptor double KO mice as novel experimental tools. Specifically, we examined the ability of the muscarinic agonist carbachol to stimulate amylase secretion in vitro, using dispersed pancreatic acini prepared from wild-type and mAChR mutant mice. Quantitative reverse transcription-polymerase chain reaction studies using RNA prepared from mouse pancreatic acini showed that deletion of the M 1 or M 3 mAChR genes did not lead to significantly altered mRNA levels of the remaining mAChR subtypes. Moreover, immunoprecipitation studies with M 1 and M 3 mAChR-selective antisera demonstrated that both mAChR subtypes are expressed by mouse pancreatic acini. Strikingly, carbachol-induced stimulation of amylase secretion was significantly impaired in acinar preparations from both M 1 and M 3 receptor single KO mice and abolished in acinar preparations from M 1 /M 3 receptor double KO mice. However, another pancreatic secretagogue, bombesin, retained its ability to fully stimulate amylase secretion in acinar preparations from M 1 /M 3 receptor double KO mice. Together, these studies support the concept that cholinergic stimulation of pancreatic amylase secretion is mediated by a mixture of M 1 and M 3 mAChRs and that other mAChR subtypes do not make a significant contribution to this activity. These findings clarify the long-standing question regarding the molecular nature of the mAChR subtypes mediating the secretion of digestive enzymes from the exocrine pancreas.

Differential Coupling of Muscarinic M1, M2, and M3Receptors to Phosphoinositide Hydrolysis in Urinary Bladder and Longitudinal Muscle of the Ileum of the Mouse

“…A small amount of M 1 receptors (Wall et al, 1991) and mRNA (Maeda et al, 1988) has been detected in wild-type intestinal smooth muscle from rats, which could account for the muscarinic phosphoinositide response observed here. No compensatory increases in muscarinic receptor expression have been detected in muscarinic receptor knockout mice (Gautam et al, 2005), and evidence for a decrease in expression has actually been observed in brain (Oki et al, 2005). It would be difficult to ascribe potential changes in other signaling proteins in M 2 /M 3 knockout mice to the small M 1 response that we observed.…”

Protein kinase D1 mediates NF-κB activation induced by cholecystokinin and cholinergic signaling in pancreatic acinar cells

“…CCK-8 or CCh induced PKD1 phosphorylation and activation at the concentration as low as 0.1 nM or 1 M, respectively, a physiological level of CCK-8 or CCh that causes maximal digestive enzyme secretion. The maximal effects of these agonists on PKD1 were achieved at 10 -100 nM CCK-8 or at 100 -1,000 M CCh, i.e., at their supramaximal concentrations that cause inhibition of enzyme secretion and activation of the inflammatory response (2,8,9,51). These results indicate that PKD1 is activated by CCK-8 and CCh at both physiological and pathological doses.…”

Single-cell transcriptomes identify human islet cell signatures and reveal cell-type–specific expression changes in type 2 diabetes

“…Elevated FEV, TPH1, and SLC6A4 expression suggests PP/ gamma cells share a suite of characteristic genes with serotonergic neurons that, in the pancreas, integrate central and peripheral hunger and satiety cues. We also observed high PP/gamma expression of muscarinic acetylcholine receptor M3, CHRM3, which stimulates exocrine pancreatic amylase (Gautam et al 2005), insulin secretion (Kong and Tobin 2011;Molina et al 2014), and smooth muscle contraction and gastric emptying (Eglen et al 1994). These data implicate the less abundant delta and PP/gamma cell types as critical for islet function via the integration of systemic cues and warrant further studies to elucidate the function and health of these cells in normal and diabetogenic conditions.…”