Sphingomyelinase selectively reduces M1 muscarinic receptors in rat hippocampal membranes.
Although there is evidence that nicotinic acetylcholine (Ach) receptors are influenced by ceramides, we do not currently know whether or not these sphingolipids can also regulate the muscarinic subtypes of Ach receptors. Using the whole-cell patch technique, we demonstrated that the effectiveness of the muscarinic receptor agonist pilocarpine, in enhancing spontaneous inhibitory postsynaptic currents in CA1 pyramidal cells, was completely abolished in hippocampal slices pre-exposed to the ceramide-generating enzyme sphingomyelinase (SMase). Western blot experiments, performed with biotinylated hippocampal membranes, showed that this electrophysiological defect possibly relies on the loss of M1 muscarinic Ach receptors at the cell surface. However, the effect appears to be relatively specific as the cell-surface expression of M4 muscarinic receptors was not found to be impacted by SMase treatment. Interestingly, we observed that G protein-coupled receptor kinases 2 and β-arrestin1/2 interactions with M1-immunoprecipitated proteins were substantially augmented in SMase-treated slices and that the reduction of cell-surface M1 muscarinic receptor expression generated was completely suppressed by the muscarinic antagonist atropine. Collectively, our data suggest that selective internalization of M1 muscarinic receptors can be accentuated in neurons subjected to high ceramide levels. The potential physiopathological implications of this finding are presented.
Groupe de recherche en Neuroscience, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada.
Eve
E
Dontigny
Christian
C
Patenaude
Michel
M
Cyr
Guy
G
Massicotte
D000818:Animals; D019390:Arrestins / Q000378:metabolism; D001640:Bicuculline / Q000494:pharmacology; D019921:Biotinylation; D002462:Cell Membrane / Q000187:drug effects*; D004347:Drug Interactions; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000378:metabolism; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D006624:Hippocampus / Q000166:cytology* / Q000187:drug effects; D047468:Immunoprecipitation; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010862:Pilocarpine / Q000494:pharmacology; D017966:Pyramidal Cells / Q000166:cytology* / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043643:Receptor, Muscarinic M1 / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology*; D013997:Time Factors; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology; D000071557:beta-Arrestins
D019390:Arrestins; D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D018721:Muscarinic Agonists; D011810:Quinoxalines; D043643:Receptor, Muscarinic M1; D000071557:beta-Arrestins; D010862:Pilocarpine; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C056639:2-amino-5-phosphopentanoic acid; C496569:Grk2 protein, rat; D054769:G-Protein-Coupled Receptor Kinase 2; D013108:Sphingomyelin Phosphodiesterase; D014633:Valine; D001640:Bicuculline