MUSCARINIC RECEPTORS IN ISOLATED GUINEA-PIG PANCREATIC DUCTS

Biochemical and pharmacological characteristics of muscarinic choliner gic receptors in isolated guinea pig pancreatic ducts were determined in the present study. Duct homogenates bound 6.82 +/- 0.69 fmol of H- 3!N-methylscopolamine (H-3!NMS)/mug of DNA with a K(d) of 0.73 +/- 0. 05 nM. The density of H-3!NMS binding sites in the excretory ducts wa s seven times greater than that in acini from the same pancreases. Com petition binding studies with atropine, pirenzepine, -piperidinyl!acet yl!-5,11-dihydro-6H-pyrido2,3-b! 1,4!benzodiazepine-6-one (AF-DX 116 ), and 4-diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP) indic ated that both M2 and M3 subtypes of muscarinic receptors are present in these preparations of isolated pancreatic ducts. Electrophoretic an alysis of H-3!propylbenzilylcholine mustard-labeled unreduced and red uced duct muscarinic receptors provided molecular mass estimates of 62 .6 +/- 2.5 and 58.0 +/- 1.6 kDa, respectively. Deglycosylation of duct al muscarinic receptors with N-glycanase decreased their apparent mole cular mass by approximately 4 kDa. These results demonstrate that isol ated pancreatic ducts express both M2 and M3 muscarinic receptors, wit h the former subtype predominating.