Muscarinic receptors in the stomach

Using tritiated N-methyl-scopolamine (3H-NMS), muscarinic receptor binding was demonstrated in broken cell preparation of mucosa and smooth muscle of the fundus of the canine stomach. Binding curves of pirenzepine were established in competition experiments against 3H-NMS. Pirenzepine shows a considerably higher affinity to muscarinic receptors from fundic mucosa than those from smooth muscle, suggesting a difference of muscarinic receptors in these two regions of the stomach. Different properties of mucosal and smooth muscle receptors could be further substantiated by agonist binding studies. Whilst carbachol binding to muscarinic receptors from fundic smooth muscle was modulated by guanine nucleotides, no such effect was found in fundic mucosa. Direct binding studies with 3H-NMS demonstrated muscarinic receptors in peripheral ganglia (sympathetic trunk ganglia from the calf, stellate ganglia from the dog). These are characterized by high affinity pirenzepine binding so that besides its direct action on gastric secretory glands, pirenzepine may influence indirectly gastrointestinal functions via peripheral, presumably intramural, ganglia.