What are the three mechanisms of ACh signal transduction for muscarinic receptors?

The mechanisms of acetylcholine (ACh) signal transduction for muscarinic receptors primarily involve the activation of phospholipase C, the decrease of adenylyl cyclase activity, and the involvement of second messengers.

Muscarinic receptors, which are G protein-coupled receptors (GPCRs), can trigger a variety of intracellular responses upon binding ACh. When ACh binds to these receptors, it can activate certain G proteins that stimulate phospholipase C. This enzyme catalyzes the production of inositol trisphosphate (IP3) and diacylglycerol (DAG), which are critical second messengers involved in cellular signaling pathways, leading to increased intracellular calcium levels and various physiological effects.

Additionally, muscarinic receptors can inhibit adenylyl cyclase, which results in decreased levels of cyclic AMP (cAMP) in the cell. This action contrasts with some other receptor types that might stimulate adenylyl cyclase, illustrating the diverse roles that different types of receptors play in cellular signaling.

Second messengers like IP3, DAG, and calcium ions then propagate the signaling cascade to produce the desired cellular responses. This complex interaction underpins many of the physiological effects