receptor
Meaning of receptor: The lock a hormone, drug or nerve signal must fit before a cell will act on the message it carries.
Definition of receptor
A receptor is a protein that recognizes one particular signaling molecule and changes the cell's behavior when that molecule attaches to it. Some receptors sit in the outer membrane and catch signals arriving from outside. Others sit deep in the cytoplasm or the nucleus and bind small molecules able to cross the membrane. The fit is specific, like a key in one lock.
What happens when a signal binds?
The signaling molecule, called a ligand, settles into a pocket shaped to hold it. Binding alters the receptor's shape, and that shape change is the message. What follows depends on the kind of receptor. Some are channels that swing open and let charged particles pour across the membrane, which is how nerve and muscle cells respond within milliseconds. Some are enzymes that switch on and begin tagging other proteins. Some hand the signal to a relay protein inside the cell, which sets off a cascade of further steps. In each case a small event outside the cell is amplified into a large response within it.
What are the main types?
| Where it sits | How it acts | Example |
|---|---|---|
| Surface, ion channel | Opens a pore for charged particles | Nicotinic acetylcholine receptor |
| Surface, G protein coupled | Passes the signal to a relay protein | Adrenaline receptors |
| Surface, enzyme linked | Switches on a built-in enzyme | Insulin receptor |
| Inside the cell | Travels to DNA and alters gene activity | Steroid hormone receptors |
Why do receptors matter in medicine?
Most medicines act on a receptor. An agonist binds and switches it on, imitating the natural signal. An antagonist, or blocker, binds without switching anything on and keeps the natural signal out. Beta blockers, antihistamines and opioid painkillers are all named for the receptor they occupy. Receptors also serve as markers on tumor tissue. Testing breast cancer tissue for the estrogen receptor shows whether the growth depends on that hormone, and a hormone receptor result of that kind determines which treatments can work at all.
Do receptors change over time?
They do. Constant heavy stimulation makes a cell pull receptors back from its surface or reduce how strongly they respond, a process called downregulation. It is one reason a drug can lose its effect during continued use. The reverse also happens: prolonged blockade leaves extra receptors on the surface, so stopping a blocker abruptly can leave the cell unusually sensitive to the natural signal.
Used in a sentence
The tumor tissue was tested for hormone receptor expression before treatment was selected.
Good to know
A receptor decides which cells respond to a signal, so a hormone circulating through the whole body affects only the tissues that carry the matching receptor.
Word origin
Where “receptor” comes from
From the Latin recipere, meaning to receive, through receptor, one that receives.