Disease relevance of Chrm4

• A CHO-K1 cell line transfected with the human m2 receptor was used as a homogeneous M2 tissue for comparison with two putative M4 systems (rat striatum and the N1E-115 mouse neuroblastoma cell line) [1].
• Pertussis toxin was used to block effects mediated by M2 and M4 receptors [2].

High impact information on Chrm4

• RGS4-dependent attenuation of M4 autoreceptor function in striatal cholinergic interneurons following dopamine depletion [3].
• A chimeric protein in which the region from M1 to M4 of the alpha subunit was replaced by the corresponding region in the beta subunit was unable to support AChR assembly when substituted for the alpha subunit; a chimeric alpha subunit containing only the long cytoplasmic loop from the beta subunit was likewise inactive [4].
• By constructing chimeras composed of segments of the epsilon and gamma subunits, we show that the main determinant of this kinetic change is a 30 residue segment of a predicted amphipathic helix located between transmembrane domains M3 and M4 [5].
• Together these results suggest a crucial role for muscarinic M2 and M4 receptors in the tonic and phasic regulation of acetylcholine efflux in the hippocampus as well as in cognitive processes [6].
• The fourth transmembrane domain (M4) of the nicotinic acetylcholine receptor (AChR) contributes to the kinetics of activation, yet its close association with the lipid bilayer makes it the outermost of the transmembrane domains [7].

Biological context of Chrm4

• In the M1-M4 KO mice, the number of [3H]NMS binding sites (Bmax) was decreased throughout the central nervous system (CNS) with significant regional differences [8].
• We propose that M4 receptor agonists could represent an innovative strategy for the treatment of pathologies associated with hyperdopaminergia [9].
• To study changes in alpha4beta2 receptor levels and assembly during this upregulation, we incorporated yellow and cyan fluorescent proteins (YFPs and CFPs) into the alpha4 or beta2 M3-M4 intracellular loops, and these subunits were coexpressed in human embryonic kidney (HEK) 293T cells and cultured ventral midbrain neurons [10].

Anatomical context of Chrm4

• These results indicate that both M2 and M4 receptors mediate the muscarinic autoinhibition in ACh release in the LMMP preparation of the mouse ileum, and loss of one of these subtypes can be compensated functionally by a receptor that remained [11].
• Our results collectively suggest that M1 receptor was present in a relatively high density in the cerebral cortex and hippocampus, and the densities of M1 and M4 subtypes were highest in the corpus striatum [8].
• Opposing functions of spinal M2, M3, and M4 receptor subtypes in regulation of GABAergic inputs to dorsal horn neurons revealed by muscarinic receptor knockout mice [12].
• 3-(2-Hydroxyethyl)-3-[4,5-(3)H(2)]-n-pentyldiazirine photoincorporated into Torpedo nAcChoR-rich membranes mainly in the alpha subunit with 70% being in a proteolytic fragment containing the M4 transmembrane segment [13].
• Novel signaling pathways mediating reciprocal control of keratinocyte migration and wound epithelialization through M3 and M4 muscarinic receptors [14].

Associations of Chrm4 with chemical compounds

• Roles of M2 and M4 muscarinic receptors in regulating acetylcholine release from myenteric neurons of mouse ileum [11].
• In M2 and M4 receptor double KO mice, the amount of EFS-induced ACh release was equivalent to an atropine-evoked level in the wild-type mouse, and further addition of atropine had no effect [11].
• M4 mAChRs modulate dopamine activity in motor tracts and act as inhibitory autoreceptors in striatum [15].
• In M2 or M4 single-KO mice, oxotremorine-M produced a variable effect on sIPSCs; it increased the frequency of sIPSCs in some cells but decreased the sIPSC frequency in other neurons [12].
• These results show regions within the N-terminal domain that are involved in gating-dependent conformational shifts, confirm that the cysteine loop resides at or near the protein-membrane interface, and show that segments of the M3-M4 loop are near to the lipid bilayer [16].

Regulatory relationships of Chrm4

• KC migration and wound reepithelialization were facilitated by M4 and inhibited by M3 [14].
• This observation is consistent with the concept that M4 receptors exert inhibitory control over D1 receptor-mediated locomotor stimulation, probably at the level of striatal projection neurons where the two receptors are known to be coexpressed [17].

Other interactions of Chrm4

• M4 receptor immunoreactivity was located in the enteric neurons, being in co-localization with M2 receptor immunoreactivity [11].
• Early in development, the M4 receptor is the predominant mAChR while the levels of the M2 and M3 receptors increase later in development [18].
• M4 codes for a transmembrane G protein that functions to transduce the action of acetylcholine neural transmitters in the nervous system [19].
• However, M4 receptor-deficient mice showed an increase in basal locomotor activity and greatly enhanced locomotor responses following drug-induced activation of D1 dopamine receptors [17].

Analytical, diagnostic and therapeutic context of Chrm4

• Microdialysis delivery of 3 nM AF-DX 116, a muscarinic antagonist with relatively high affinity for the M2 and M4 subtypes, significantly (P < 0.01) increased prefrontal cortical ACh release and activated EEG in the contralateral prefrontal cortex [20].
• To explore the physiological roles of the two Gi-coupled muscarinic receptors, we disrupted the M2 and M4 receptor genes in mice by using a gene targeting strategy [17].
• Using in vivo microdialysis, we found elevated dopamine (DA) basal values and enhanced DA response to psychostimulants in the nucleus accumbens of M4 knockout mice [9].
• 2. PCR amplification of genomic DNA confirmed that the BALB/C mouse alpha subunit gene has a T nucleotide at position 1306, and, therefore, that the protein has a V at position 433 in the M4 segment [21].

References