mAChR M3 Inhibitors

Muscarinic Acetylcholine Receptors (mAChRs) are a class of G protein-coupled receptors (GPCRs) that play a crucial role in mediating the effects of the neurotransmitter acetylcholine (ACh) in the central nervous system (CNS) and peripheral tissues. These receptors are named after muscarine, a natural alkaloid compound found in certain mushrooms, which can selectively activate them. There are five subtypes of mAChRs, designated as M1 through M5, each encoded by a distinct gene. These receptor subtypes exhibit distinct anatomical distribution patterns and signaling mechanisms, allowing for diverse physiological responses to acetylcholine. mAChRs are integral membrane proteins composed of seven transmembrane helices (TMHs) connected by intracellular and extracellular loops. They are primarily found on the plasma membrane of postsynaptic neurons, smooth muscles, and other cell types throughout the body. Additionally, some mAChRs are also present in presynaptic terminals, where they regulate neurotransmitter release. Upon binding acetylcholine, mAChRs undergo conformational changes that activate their intracellular signaling pathways. Activation of mAChRs leads to the dissociation of the heterotrimeric G proteins into Gα and Gβγ subunits. The Gα subunit then modulates the activity of various effector proteins, such as ion channels and enzymes, resulting in diverse physiological responses.The different mAChR subtypes display varying affinities for acetylcholine and selective agonists or antagonists. For instance, M1, M3, and M5 subtypes primarily couple to Gq/11 proteins, which activate phospholipase Cβ (PLCβ) and subsequently elevate intracellular calcium levels and activate protein kinase C (PKC). On the other hand, M2 and M4 subtypes predominantly couple to Gi/o proteins, which inhibit adenylate cyclase (AC) and reduce cyclic AMP (cAMP) levels, leading to downstream effects mediated by cAMP-dependent protein kinase (PKA). Due to their extensive distribution and involvement in various physiological processes, mAChRs have profound effects on the nervous, cardiovascular, respiratory, gastrointestinal, and urinary systems.