Histamine receptors are G protein-coupled receptors found on different cell types, stimulated by histamine molecules outside the cell. There are four types of histamine receptors: H1, H2, H3, and H4, each causing different reactions within different cells. Antihistamines block the activity of H1 and H2 receptors and are commonly used in allergy and acid reflux medications.
There are four different types of histamine receptors found in the body. All four are similar in that they are G protein-coupled receptors. Each histamine receptor is found on different cell types and has different ways of signaling the cells it is found on.
G protein-coupled receptors are transmembrane receptors, which means they cross the cell membrane. Histamine receptors are stimulated by histamine molecules outside the cell. When a histamine receptor is activated, it sends a signal into the cell. This signal then causes a specific response from the cell, based on which type of cell is being stimulated.
Histamine is a naturally occurring molecule created by all tissues in the body, although it is much more prevalent in some than in others. It is well known for the role it plays in allergic reactions, but it is also important for many normal processes within the body. The histamine receptor is what determines the sensitivity, as well as the response, of the cell to histamine.
The four types of histamine receptors that have been identified are the H1, H2, H3 and H4 receptors. These four receptors are one of the reasons histamine causes such a wide range of symptoms. Each receptor is stimulated by histamine, but causes different reactions within different cells.
The H1 histamine receptor is found throughout the body. Specifically, H1 receptors are found in smooth or involuntary muscle cells, the cells that line blood vessels in the heart and central nervous system. When stimulated, H1 receptors control smooth muscle contraction and blood vessel dilation. Overstimulation causes an acute allergic reaction.
In comparison, histamine H2 receptors are found predominantly in the parietal cells of the stomach. These cells are responsible for the secretion of gastric acid when stimulated by histamine. H3 receptors are found within the central nervous system and regulate the release of neurotransmitters in the brain. Finally, H4 receptors are found primarily in cells of the immune system, including T lymphocytes, mast cells, and eosinophils. These receptors play a role in how the body’s immune responses are regulated.
Antihistamines have been developed, i.e. drugs that block the action of histamine, which counteract the activity of the H1 and H2 receptors. Antihistamines that block the activity of histamine H1 receptors are commonly used in allergy medications, as well as cold medications and sleeping pills. Drugs that have been developed to block H2 receptors are used to treat acid reflux, as they inhibit the secretion of stomach acid.
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