Muscarinic receptors

Muscarinic receptors are a type of receptor that are activated by the neurotransmitter acetylcholine. They are named after the compound muscarine, which can activate these receptors in the absence of acetylcholine. Muscarinic receptors are found in many parts of the body, including the brain, heart, and smooth muscle tissue.

Structure

Muscarinic receptors are a type of G protein-coupled receptor (GPCR), which means they have seven transmembrane domains. The binding site for acetylcholine is located in the extracellular portion of the receptor.

Function

When acetylcholine binds to a muscarinic receptor, it causes a conformational change in the receptor that allows it to activate a G protein. This in turn triggers a series of events inside the cell that can lead to various responses, depending on the type of cell and the specific type of muscarinic receptor involved.

Types

There are five known types of muscarinic receptors, designated M1 through M5. Each type is found in different tissues and has different effects when activated.

• M1 receptors are found in the brain and parasympathetic nervous system, where they play a role in learning and memory.
• M2 receptors are found in the heart, where they help to slow the heart rate.
• M3 receptors are found in smooth muscle tissue and glands, where they help to stimulate muscle contraction and gland secretion.
• M4 receptors are found in the brain, where they play a role in controlling movement.
• M5 receptors are found in the brain and blood vessels, where they help to regulate blood flow.

Clinical significance

Because muscarinic receptors play a role in many different bodily functions, drugs that target these receptors can be used to treat a variety of conditions. For example, drugs that block muscarinic receptors in the lungs can be used to treat asthma and chronic obstructive pulmonary disease (COPD), while drugs that stimulate muscarinic receptors in the bladder can be used to treat overactive bladder.

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