MUSCARINIC RECEPTORS IN ISOLATED GUINEA-PIG PANCREATIC DUCTS

Biochemical and pharmacological characteristics of muscarinic cholinergic 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 was seven times greater than that in acini from the same pancreases. Competition binding studies with atropine, pirenzepine, 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b] [1,4]benzodiazepine-6-one (AF-DX 116), and 4-diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP) indicated that both M2 and M3 subtypes of muscarinic receptors are present in these preparations of isolated pancreatic ducts. Electrophoretic analysis of [H-3]propylbenzilylcholine mustard-labeled unreduced and reduced duct muscarinic receptors provided molecular mass estimates of 62.6 +/- 2.5 and 58.0 +/- 1.6 kDa, respectively. Deglycosylation of ductal muscarinic receptors with N-glycanase decreased their apparent molecular mass by approximately 4 kDa. These results demonstrate that isolated pancreatic ducts express both M2 and M3 muscarinic receptors, with the former subtype predominating.