CHRM - Muscarinic acetylcholine receptor | Elisa - Clia - Antibody - Protein

Muscarinic Receptors (CHRM)

Muscarinic receptors, also known as cholinergic receptors, are a class of G protein-coupled receptors (GPCRs) that respond to the neurotransmitter acetylcholine. They play essential roles in the parasympathetic nervous system, regulating various physiological processes, including heart rate, smooth muscle contraction, glandular secretion, and neuronal signaling.

Structural Features

Muscarinic receptors, like other GPCRs, possess seven transmembrane domains, an extracellular N-terminus, and an intracellular C-terminus. Upon ligand binding, conformational changes in the receptor initiate intracellular signaling cascades through interaction with heterotrimeric G proteins.

Subtypes and Classification

Muscarinic receptors are classified into five subtypes, designated as M1 (CHRM1) through M5 (CHRM5), based on their pharmacological properties and downstream signaling pathways:

M1 Receptor (CHRM1): Predominantly expressed in the central nervous system (CNS), particularly in regions involved in cognitive function and memory, such as the hippocampus and cerebral cortex.

M2 Receptor (CHRM2): Found in various tissues, including the heart, smooth muscle, and CNS, where it regulates cardiac function, smooth muscle contraction, and neurotransmitter release.

M3 Receptor (CHRM3): Expressed in glandular tissues, smooth muscle, and endothelial cells, where it mediates glandular secretion, smooth muscle contraction, and vasodilation.

M4 Receptor (CHRM4): Present in the CNS, particularly in areas involved in motor control and mood regulation, such as the striatum and limbic system.

M5 Receptor (CHRM5): Widely distributed in the CNS, where its precise functions are still being elucidated.

Ligands

Muscarinic receptors are activated by the neurotransmitter acetylcholine, which is released by cholinergic neurons in the parasympathetic nervous system and by certain neurons in the sympathetic nervous system. Muscarinic receptors also interact with exogenous ligands, including muscarinic agonists and antagonists used in pharmacotherapy. They mediate various physiological effects in different tissues and organ systems:

Cardiovascular System: Muscarinic receptors regulate heart rate, cardiac contractility, and vascular tone, with M2 receptors predominating in the heart and M3 receptors mediating vasodilation.

Smooth Muscle Contraction: Muscarinic receptors modulate smooth muscle contraction in various organs, including the gastrointestinal tract, urinary bladder, and respiratory system, influencing processes such as peristalsis, urination, and bronchoconstriction.

Glandular Secretion: Muscarinic receptors stimulate glandular secretion in exocrine glands, including salivary glands, lacrimal glands, and sweat glands, promoting the production and release of saliva, tears, and sweat.

Neuronal Signaling

Muscarinic receptors modulate neuronal excitability, synaptic transmission, and neurotransmitter release in the CNS, contributing to cognitive function, memory formation, and motor control.

Clinical Implications

Dysregulation of muscarinic receptor signaling is associated with various pathological conditions:

Cardiovascular Disorders: Altered muscarinic receptor activity may contribute to cardiovascular disorders such as bradycardia, atrioventricular block, and vasovagal syncope.

Respiratory Disorders: Dysfunction of muscarinic receptor signaling is implicated in respiratory disorders such as asthma, chronic obstructive pulmonary disease (COPD), and bronchitis.

Gastrointestinal Disorders: Changes in muscarinic receptor expression or function may be involved in gastrointestinal disorders such as irritable bowel syndrome (IBS), gastroparesis, and peptic ulcer disease.

Neurological Disorders: Dysfunctional muscarinic receptor signaling is associated with neurological disorders such as Alzheimer's disease, Parkinson's disease, and schizophrenia.