Types of Receptors

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Chapter: Medicinal Chemistry : Receptors

There are four types of receptors. Type 1: Ligand-gated ion channels , Type 2: G-protein-coupled receptors , Type 3: Kinase-linked receptors , Type 4: Nuclear receptors


TYPES OF RECEPTORS

Receptors elicit many different types of cellular effect. Some of them are very rapid, that is, those involved in synaptic transmission, operating within milliseconds, and other receptors for hormones that operates after hours and days. There are four types of receptors.

Type 1: Ligand-gated ion channels 

Type 2: G-protein-coupled receptors 

Type 3: Kinase-linked receptors 

Type 4: Nuclear receptors

Ligand-gated ion channels: The ligand-gated ion channels are also known as ionotropic receptors. These are membrane proteins with a similar structure to other ion channels, but incorporating a ligand-binding site (receptor), usually in an extracellular domain. Typically, these are the receptors on which fast neurotransmitters act.

Examples: nicotinic acetylcholine receptor, GABAA receptor, and glutamate receptor of N-methyl-D-aspartic acid (NMDA).

G-protein-coupled receptors: It is also called metabotropic receptors or seven-trans membrane spanning receptors that act through a second messenger, which elicits an action. Second messengers usually are cyclic adenosine monophosphate (cAMP) and inositol trisphosphate (IP3).

Examples: muscarnic receptors, beta adrenergic receptors, serotonin receptors and opioid receptors.

Kinase-linked or enzyme-linked receptors: These constitute extracellular ligand-binding domain that is linked to an intracellular domain by a single transmembrane helix. In many cases, the intracellular domain is enzymatic in nature. Some times the receptor subunit may bind to an enzyme called Janus-Kinase. Type 3 receptors include those for insulin and various cytokines.

Nuclear receptors: The nuclear receptors regulate the gene transcriptions, are located in the cytosol, and migrate to the nuclear compartment when a ligand is present. The receptor protein is inherently capable of binding to speciļ¬c genes. These include the receptors of glucocorticoids and thyroid hormone.

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