Telenzepine-sensitive muscarinic receptors on rat pancreatic acinar cells

Abstract

. Telenzepinesensitive muscarinic receptors on rat pancreatic acinar cells. Am. J. Physiol. 274 (Gastrointest. Liver Physiol. 37): G734-G741, 1998.-To identify the muscarinic subtype present on the rat pancreatic acinar cell, we examined the effects of different muscarinic receptor antagonists on amylase secretion and proteolytic zymogen processing in isolated rat pancreatic acini. Maximal zymogen processing required a concentration of carbachol 10-to 100-fold greater (10 Ϫ3 M) than that required for maximal amylase secretion (10 Ϫ5 M). Although both secretion and conversion were inhibited by the M3 antagonist 4-diphenylacetoxy-N-methyl-piperidine (4-DAMP) (50% inhibition ϳ6 ϫ 10 Ϫ7 M and 1 ϫ 10 Ϫ8 M, respectively), the most potent inhibitor was the M1 antagonist telenzepine (50% inhibition ϳ5 ϫ 10 Ϫ10 M and 1 ϫ 10 Ϫ11 M, respectively). Pirenzepine, another M1 antagonist, and the M2 antagonist methoctramine did not reduce amylase secretion or zymogen processing in concentrations up to 1 ϫ 10 Ϫ5 M. Analysis of acinar cell muscarinic receptor by PCR revealed expression of both m1 and m3 subtypes. The pancreatic acinar cell has a distinct pattern of muscarinic antagonist sensitivity (telenzepine : 4-DAMP Ͼ pirenzepine) with respect to both amylase secretion and zymogen conversion. muscarinic antagonist; 4-diphenylacetoxy-N-methyl-piperidine; carboxypeptidase A 1 ; secretion NEUROHUMORAL STIMULATION of the exocrine pancreas generates a number of physiological responses, including enhanced zymogen secretion. Recent studies suggest that cholinergic pathways may have a more important role in regulating pancreatic secretion than previously appreciated. Thus the primary action of CCK released by the intestinal nutrients may be to stimulate the cholinergic release of acetylcholine (ACh) (1, 16). The neurotransmitter then acts on muscarinic ACh receptors (mAChR) to stimulate acinar cell secretion. Cholinergic pathways may play a role in pathological processes such as the proteolytic processing of zymogens to active forms.Cholinergic stimulation may contribute to the pathogenesis of pancreatitis such as that induced by the bite of the Tityus serrulatus scorpion (22), alcohol-associated disease, and cholinesterase inhibitors (17). A key step for initiating many forms of pancreatitis appears to be the pathological intracellular activation of digestive zymogens (15). In vivo studies that use supramaximal concentrations (10-to 100-fold greater than that generating a maximal secretory response) of CCK or cholinergic agonists generate acute pancreatitis (9) and zymogen activation (18). Likewise, hyperstimulation of isolated pancreatic acini by CCK leads to the rapid activation of proteases and enhanced zymogen processing (15). The protease activation observed in isolated pancreatic acini may be relevant to the pathogenesis of acute pancreatitis.The identification of the muscarinic receptors on the pancreatic acinar cell is relevant to pancreatic physiology and pathology. Muscarinic antagonists are most often used to establish the...

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

“…However, in the present study we provide unambiguous evidence that cholinergic activation of pancreatic digestive enzyme (amylase) secretion is mediated by a mixture of M 1 and M 3 mAChRs, at least in the mouse. Several years ago, Schmid et al (1998) reported that the M 1 receptor-preferring antagonist telenzepine (a pirenzepine analog) was about 1000 times more potent than 4-DAMP in inhibiting carbachol-induced amylase secretion in rat pancreatic acini. However, 4-DAMP (Dörje et al, 1991;Caulfield and Birdsall, 1998) and telenzepine (Schudt et al, 1989;Lazareno et al, 1990;Karton et al, 1991) are known to bind to M 1 receptors with similar affinities (K i ϳ 1-3 nM), and even high concentrations of the classical M 1 receptor-preferring antagonist pirenzepine had no effect on carbachol-induced amylase secretion (Schmid et al, 1998).…”

“…Interestingly, recent RT-PCR studies have shown that rat pancreatic acini not only express M 3 but also M 1 mAChR mRNA (Schmid et al, 1998;Turner et al, 2001). To examine whether both acinar M 1 and M 3 receptors play a role in cholinergic stimulation of exocrine pancreas secretion, we used M 1 Fisahn et al, 2002) and M 3 receptor single KO mice ) and recently generated M 1 /M 3 receptor double KO mice as novel experimental tools.…”

The ryanodine receptor mediates early zymogen activation in pancreatitis

“…Physiologic agonist stimulation is associated with maximal enzyme secretion and minimal zymogen activation; supraphysiologic stimulation reduces secretion and causes pathologic zymogen activation (38). Inhibiting RYR Ca 2ϩ release during physiologic stimulation has been shown to diminish the basolateral component of the Ca 2ϩ wave but does not affect its capacity to elicit maximal enzyme secretion (36).…”

Cholinergic agonist-induced pepsinogen secretion from murine gastric chief cells is mediated by M1and M3muscarinic receptors

“…For example, previous studies have indicated coexpression of M 1 and M 3 receptors in rat striatum (36) and sublingual glands (7). Moreover, in rat pancreatic acinar cells that have receptors and signal transduction pathways very similar to those described for gastric chief cells (25), pharmacological and PCR analysis was consistent with the presence of both M 1 and M 3 receptors (33).…”

“…However, none of these studies excluded the possibility that chief cells coexpress M 1 and M 3 receptors. For example, pharmacological and PCR analysis of muscarinic receptor expression in dispersed acini from rat pancreas are consistent with expression of both M 1 and M 3 muscarinic receptors (33). It is of interest that the cellular biology of the gastric chief cell and pancreatic acinar cell is very similar (25).…”