scholarly journals Agonist-induced desensitization and phosphorylation of m1-muscarinic receptors

1999 ◽  
Vol 338 (1) ◽  
pp. 175-183 ◽  
Author(s):  
Mark G. WAUGH ◽  
R. A. John CHALLISS ◽  
Gabriel BERSTEIN ◽  
Stefan R. NAHORSKI ◽  
Andrew B. TOBIN
Keyword(s):  
Muscarinic Receptor ◽  
Muscarinic Receptors ◽  
Chinese Hamster ◽  
Receptor Internalization ◽  
Receptor Subtype ◽  
Muscarinic Agonist ◽  
Dependent Manner ◽  
Receptor Desensitization ◽  
M1 Muscarinic ◽  
M1 Muscarinic Receptors

Pre-stimulation of Chinese hamster ovary (CHO) cells expressing the human m1-muscarinic receptor (CHO-m1 cells) with a maximally effective concentration of the muscarinic agonist methacholine resulted in desensitization of Ins(1,4,5)P3 accumulation, apparent as a ∼ 4-fold shift in the agonist dose–response curve. Agonist-induced desensitization was rapid (detectable by 10 s) and concentration dependent (EC50 = 8.2±2.2 µM) and resulted in a complete loss of receptor reserve for the agonist-stimulated Ins(1,4,5)P3 response. An investigation of the possible mechanisms involved in m1-muscarinic receptor desensitization indicated that agonist-induced receptor internalization, PtdIns-(4,5)P2 depletion or an increased rate of Ins(1,4,5)P3 metabolism were not involved. m1-Muscarinic receptors did, however, undergo rapid agonist-induced phosphorylation with a time course that was consistent with an involvement in receptor desensitization. Characterization studies indicated that the receptor-specific kinase involved was distinct from protein kinase C and other second-messenger-dependent protein kinases. Since previous studies have suggested that the m3-muscarinic receptor subtype undergoes agonist-dependent phosphorylation via casein kinase 1α (CK1α) [Tobin, Totty, Sterlin and Nahorski (1997) J. Biol. Chem. 272, 20844–20849], we examined the ability of m1-muscarinic receptors to be phosphorylated by this kinase. In reconstitution experiments, CK1α was able to phosphorylate purified, soluble m1-muscarinic receptors in an agonist-dependent manner.

Halothane Inhibits Signaling through m1 Muscarinic Receptors Expressed in Xenopus Oocytes 

1995 ◽  
Vol 82 (1) ◽  
pp. 174-182 ◽  
Author(s):  
Marcel E. Durieux
Keyword(s):  
Angiotensin Ii ◽  
Protein Interactions ◽  
Intracellular Signaling ◽  
Xenopus Oocytes ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Muscarinic Agonist ◽  
Dependent Manner ◽  
Signaling Systems ◽  
M1 Muscarinic

Background Interactions between volatile anesthetics and muscarinic acetylcholine receptors have been studied primarily in binding assays or in functional systems derived from tissues or cells, often containing multiple receptor subtypes. Because interactions with muscarinic signaling systems may explain some effects and side effects of anesthetics and form a model for anesthetic-protein interactions in general, the author studied anesthetic inhibition of muscarinic signaling in an isolated system. Methods mRNA encoding the m1 muscarinic receptor subtype was prepared in vitro and expressed in Xenopus oocytes. Effects of halothane on methylcholine-induced intracellular Ca2+ release was measured. Angiotensin II receptors were expressed to evaluate anesthetic effects on intracellular signaling. Results m1 Receptors expressed in oocytes were functional, and could be inhibited by atropine and pirenzepine. Halothane depressed m1 muscarinic signaling in a dose-dependent manner: half-maximal inhibition of 10(-7) M methylcholine was obtained with 0.3 mM halothane. The effect was reversible and could be overcome by high concentrations of muscarinic agonist. Angiotensin II signaling was unaffected by 0.34 mM halothane. Conclusions m1 Muscarinic signaling is inhibited by halothane, and lack of halothane effect on angiotensin signaling indicates that the intracellular signaling systems of Xenopus oocytes are unaffected. Therefore, the most likely site of halothane action is the receptor and/or G protein. Oocytes provide a versatile system for detailed investigation into the molecular mechanism of anesthetic-protein interactions.

scholarly journals Fluctuating NMDA Receptor Subunit Levels in Perirhinal Cortex Relate to Their Dynamic Roles in Object Memory Destabilization and Reconsolidation

2020 ◽  
Vol 22 (1) ◽  
pp. 67
Author(s):  
Cassidy E. Wideman ◽  
James Nguyen ◽  
Sean D. Jeffries ◽  
Boyer D. Winters
Keyword(s):  
Boundary Conditions ◽  
Muscarinic Receptors ◽  
Stable State ◽  
Perirhinal Cortex ◽  
Receptor Subtype ◽  
Nmda Receptor Subunit ◽  
Object Memory ◽  
M1 Receptors ◽  
M1 Muscarinic ◽  
M1 Muscarinic Receptors

Reminder cues can destabilize consolidated memories, rendering them modifiable before they return to a stable state through the process of reconsolidation. Older and stronger memories resist this process and require the presentation of reminders along with salient novel information in order to destabilize. Previously, we demonstrated in rats that novelty-induced object memory destabilization requires acetylcholine (ACh) activity at M1 muscarinic receptors. Other research predominantly has focused on glutamate, which modulates fear memory destabilization and reconsolidation through GluN2B- and GluN2A-containing NMDARs, respectively. In the current study, we demonstrate the same dissociable roles of GluN2B- and N2A-containing NMDARs in perirhinal cortex (PRh) for object memory destabilization and reconsolidation when boundary conditions are absent. However, neither GluN2 receptor subtype was required for novelty-induced destabilization of remote, resistant memories. Furthermore, GluN2B and GluN2A subunit proteins were upregulated selectively in PRh 24 h after learning, but returned to baseline by 48 h, suggesting that NMDARs, unlike muscarinic receptors, have only a temporary role in object memory destabilization. Indeed, activation of M1 receptors in PRh at the time of reactivation effectively destabilized remote memories despite inhibition of GluN2B-containing NMDARs. These findings suggest that cholinergic activity at M1 receptors overrides boundary conditions to destabilize resistant memories when other established mechanisms are insufficient.

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