A receptor can be regarded as a biological switch. A molecule that fits attaches to it and alters the activity inside the cell. This response may be very fast, such as changes in electrical activity, or slower, involving changes in protein production.
Receptors are of importance in pharmacology because many drugs act on them. Drugs can switch a receptor on, switch it off, or change the way it responds to other molecules.
Receptor location
Receptors are located in various parts of the cell. Many are located on the cell membrane, where they detect substances outside the cell. Others are inside the cell, including in the cytoplasm or nucleus.
The location of a receptor often relates to the type of molecule it recognises. Water-soluble signalling molecules, such as many peptide hormones, generally cannot pass easily through the cell membrane. They therefore act through receptors on the cell surface.
Lipid-soluble substances can pass through the membrane more readily. Some of these interact with receptors inside the cell. Steroid hormones are a familiar example.
Cell-surface receptors can pass signals from outside the cell to the inside. Intracellular receptors can directly influence processes within the cell, including the activity of certain genes.
How does a receptor work?
Receptor activity is initiated when a molecule binds to the receptor. This molecule we often refer to as a ligand. The ligand attaches to a specific part of the receptor known as its binding site.
It’s not just physical shape; it’s the interaction. Chemical properties also affecting how strongly something binds are charge and the ability to make certain bonds.
After the binding occurs, the receptor may change its shape. The change can trigger a cascade of events inside the cell. For example, a receptor on the membrane may activate another protein which then influences an enzyme or makes a chemical messenger within the cell.
This process is known as signal transduction. It allows a relatively small event at the receptor to produce a wider cellular response.
The response depends on the receptor, the cell type and the signalling pathway involved. The same receptor can sometimes produce different effects in different tissues.
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Receptors and medicines
Receptors are a major focus of drug development. Many medicines produce their effects by interacting with specific receptors.
A drug that activates a receptor is called an agonist. An agonist can produce a response similar to that caused by the body’s own signalling molecule, although the strength and duration of the response may differ.
A drug that binds to a receptor and prevents it from being activated is called an antagonist. It can stop another molecule from producing its usual effect.
For example, some medicines used to treat high blood pressure work by blocking receptors involved in the actions of hormones such as angiotensin II. Other drugs act on receptors involved in pain, inflammation, mood, heart rate and many other physiological processes.
Not every drug needs to bind to a receptor to have an effect. Some medicines act on enzymes, transport proteins, ion channels, or other biological targets.
What is receptor affinity?
Receptor affinity describes how strongly a molecule tends to bind to a receptor.
A molecule with high affinity can bind effectively at relatively low concentrations, although affinity alone does not tell us how much biological effect the molecule will produce.
In pharmacology, this distinction is important. Although a medication can attach itself firmly to a receptor, it may not be able to activate it at all. An appropriate example would be an adversary. It might attach itself firmly to a receptor without activating it.
Affinity is frequently mentioned in connection with other characteristics, such as potency and efficacy. These terms are different aspects of drug action and should not be confused with each other.
Receptor selectivity
A receptor is not always specific for one molecule. Different compounds can bind to the same receptor, sometimes with different affinities.
Selectivity is a drug’s preference for one receptor or receptor subtype over another. A medicine may be designed to selectively act mainly on a specific target, with less activity on related receptors.
This can be useful, as different receptor subtypes may be present in different tissues or produce different effects. But selectivity is typically a matter of degree rather than an absolute property. At higher concentrations a drug can interact with more targets .
This is one reason why a drug may have effects beyond the response originally intended.
Types of receptors
Receptors are classified into several major families depending on their structure and the way they transmit signals.
Cell membranes contain G-protein-coupled receptors (GPCRs), which function through G proteins. They participate in many processes such as neurotransmission, smell, hormone signalling and control of heart function.
Ligand-gated ion channels open and close due to a signalling molecule binding to them. This changes the movement of ions across the cell membrane and can alter the electrical state of the cell. Some receptors involved in rapid nerve signalling belong to this group.
Enzyme-linked receptors are membrane receptors associated with enzymes or enzymatic activity. Ligand binding can trigger signalling pathways which regulate processes such as cell growth and metabolism.
Intracellular Receptors. Intracellular receptors are found inside cells. They can affect gene expression and frequently react to lipid-soluble substances. Even though its activity is slower, it lasts longer.
Importance of receptors in research?
Researchers learn how cells talk to each other and how drugs work by studying receptors. Receptor studies may also help explain why two structurally similar compounds have different actions in the body.
In drug research, scientists may study receptor binding, receptor activation, selectivity and downstream signalling. Receptors allow molecules and cells to communicate with each other. These interactions have the ability to influence many aspects of a cell’s life including how quickly the cell will divide, whether or not it will grow, etc.
Changes in the behavior of receptors (how responsive they are) occur because of signals from within the cell. Receptor behavior can change in two ways: by changing the number of receptors on the surface of the cell; and/or by altering the responsiveness of existing receptors. This is referred to as receptor regulation. They help the body respond to hormones, neurotransmitters and other signals and are key targets for many drugs. They are distinguished by their location, structure, binding properties and signalling behaviour, all of which influence the consequences of a particular molecule binding to them.
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.