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A Putative M 3 Muscarinic Cholinergic Receptor of High Molecular Weight Couples to Phosphoinositide Hydrolysis in Human SK‐N‐SH Neuroblastoma Cells
Author(s) -
Fisher Stephen K.,
Heacock Anne M.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb03008.x
Subject(s) - pirenzepine , muscarinic acetylcholine receptor , antagonist , chemistry , receptor , methiodide , muscarinic acetylcholine receptor m1 , muscarinic acetylcholine receptor m2 , microbiology and biotechnology , muscarinic acetylcholine receptor m3 , stereochemistry , biochemistry , biology
The M 1 ‐selective (high affinity for pirenzepine) muscarinic acetylcholine receptor (mAChR) antagonist pirenzepine displaced both N ‐[ 3 H]methylscopolamine ([ 3 H]NMS) and [ 3 H]qui‐nuclidinylbenzilate from intact human SK‐N‐SH neuroblastoma cells with a low affinity ( K i = 869–1,066 nM), a result indicating the predominance of the M 2 or M 3 (low affinity for pirenzepine) receptor subtype in these cells. Whereas a selective M 2 agent, AF‐DX 116 {11–2[[2‐[(diethylamino)methyl]‐1‐piperidinyl]‐acetyl]‐5,11‐dihydro‐6 H ‐pyrido[2,3‐ b ][1,4]benzodiazepin‐6‐one} bound to the mAChRs with a very low affinity ( K i = 6.0 μ M ), 4‐diphenylacetoxy‐ N ‐methylpiperidine methiodide (4‐DAMP), an agent that binds with high affinity to the M 3 subtype, potently inhibited [ 3 H]NMS binding ( K i = 7.2 n M ). 4‐DAMP was also 1,000‐fold more effective than AF‐DX 1 16 at blocking stimulated phosphoinositide (PPI) hydrolysis in these cells. Covalent labeling studies (with [ 3 H]propylbenzilylcholine mustard) suggest that the size of the SK‐N‐SH mAChR (M r = 81.000–98,000) distinguishes it from the predominant mAChR species in rat cerebral cortex (M r =66,000), an M 1 ‐enriched tissue. These results provide the first demonstration of a neural M 3 mAChR subtype that couples to PPI turnover.