Types of Receptors | Their Role and Functions in the Body

Receptors are the sensing elements that communicate the signal from a ligand to the cell to elicit specific physiological change.

A ligand is one that can bind to the receptor and produce a specific response. This can be a drug or endogenous substance. There are four basic types of receptors like

  1. Ligand-gated ion channel receptors
  2. G-protein coupled receptors
  3. Kinase-linked receptors
  4. Nuclear receptors.

These receptors are located in the cells, tissues and help control all most all the body organs.

The ligand is the one that binds to the receptor and brings in conformational changes to produce a definite effect on the body’s physiology.

In general, most receptors have endogenous ligands or biomolecules, which can trigger a response.

Most receptors are named based on their endogenous ligands like serotonin, acetylcholine, opioid.

As per IUPHAR, there are hundreds of receptors in the body. They vary with each other regarding the changes they bring about in the body when a ligand binds.

Types of receptors in detail

Based on their molecular structure and mechanism:

  1. Ligand-gated ion channel receptors
  2. G-protein coupled receptors
  3. Kinase-linked receptors
  4. Nuclear receptors.
types of receptors
By: Nature publication

Based on their location in the body:

  1. Cell surface receptors
  2. Cytoplasmic receptors
  3. Intra-Nuclear receptors
  4. Floating receptors

Based on the physiological effect in the body

  1. Pharmacological receptors
  2. Silent receptors
  3. Orphan receptors
  4. Synaptic receptors.

Ligand-gated ion channel receptors

ionotropic receptors structure

They are also called ionotropic receptors. These receptors are the ones that have a channel through which ions can move inside and outside the cells.

They are located on the cell membrane and have a ligand-binding site towards to external surface. The ligand could be biomolecules like acetylcholine, GABA, or corresponding drugs.

Nicotinic acetylcholine receptor is one of the prominent receptors which falls into this category.

It is made of 4 different subunits named α, β, γ and δ

These receptors elicit the fastest response in microseconds/ milliseconds. They are found in the nervous system.

Ions like Sodium, chloride, calcium, and potassium move into the cell or outside through them.

These receptors coordinate body responses like a reflex action, sense of pain, touch, movements.

Examples: Nicotinic acetylcholine receptors, GABAA receptors

G-protein coupled receptors

This is the largest class of receptors. They are also called metabotropic receptors.

These receptors are also membrane-bound receptors but have their effector system in the cytoplasm.

These receptors are of 3 types as

A. Rhodopsin family

B. Secretin/glucagon family

C. Calcium sensor family

These receptors act through both ligand-gated channels and also enzyme-linked pathways.

g protein coupled receptor representation

The response through these receptors takes in a few seconds.

Ex: Muscarinic acetylcholine receptors, adrenergic receptors, few hormonal receptors fall under this category.

Kinase linked or enzymatic receptors.

These receptors are also cytoplasmic receptors but have an extra-cellular part that binds to a drug or ligand.

Their action involves enzymatic activation by phosphorylation. Then, there can be gene transcription and protein synthesis to produce the effect.

enzymatic receptor mechanism

The response time is a few hours.

There are four different types of Kinase linked receptors like

  1. Cytokine receptors.
  2. Receptors tyrosine kinases
  3. Serine/threonine kinases
  4. Guanylyl cyclase-linked receptors

Nuclear receptors

As the name indicates, these receptors are located in the nucleus of cells. They get activated when ligand molecules enter the nuclear membrane and bind with them.

nuclear receptor mechanism

Their response time is in hours to a few days.

These nuclear receptors are of two main types like

  1. Class I: Ex: Estrogen and other steroid receptors.
  2. Class II: Ex: peroxisome proliferator-activated receptor

Silent receptors: Silent receptors are those receptors to which ligands bind with high affinity, but interestingly no pharmacological effect is produced.

Ex: Plasma proteins.

Orphan receptors: These are the receptors that do not have well defined endogenous ligands. But they can produce a response when other ligands bind to them. In other words, their actual endogenous ligands have not been discovered yet. Once the endogenous ligand is identified, they will be given a specific name.

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