The main difference between adrenergic and cholinergic receptors is that adrenergic receptors selectively bind catecholamines: epinephrine and norepinephrine, whereas cholinergic receptors selectively bind acetylcholine.
Adrenergic and cholinergic receptors are two transmembrane receptors. They induce different effects on the body.
Key Areas Covered
1. What are Adrenergic Receptors
– Definition, Types, Function
2. What are Cholinergic Receptors
– Definition, Types, Function
3. Similarities Between Adrenergic and Cholinergic Receptors
– Outline of Common Features
4. Difference Between Adrenergic and Cholinergic Receptors
– Comparison of Key Differences
Key Terms
Adrenergic Receptors, Cholinergic Receptors
What are Adrenergic Receptors
Adrenergic receptors are glycoproteins that selectively bind catecholamines: epinephrine and norepinephrine released from the sympathetic nervous system and adrenal medulla. Therefore, they mediate the actions of the sympathetic nervous system. They induce arteriolar smooth muscle contraction and cardiac contraction. Critically, they involve in the homeostasis of cardiac function and blood pressure. However, activating or blocking these receptors is a major therapeutic approach in managing different cardiovascular diseases, including hypertension, cardiac arrhythmias, and angina pectoris. Beta-blockers, beta-2 (β2) agonists, and alpha-2 (α2) agonists are used to treat high blood pressure and asthma.
Figure 1: Adrenergic Receptors
Furthermore, alpha and beta receptors are the two types of adrenergic receptors. Alpha receptors control physiological processes like vasoconstriction, intestinal relaxation, and pupil dilation. The two types of alpha receptors are alpha 1 and alpha 2 receptors. Beta receptors control the relaxation of the bronchial and uterine smooth muscles and increase heart rate. These receptors are found in cardiac and smooth muscles. The stimulation of beta receptors also induces glycogenolysis in the liver and renin secretion in the kidney. The three types of beta receptors include beta 1, beta 2, and beta 3 receptors.
What are Cholinergic Receptors
Cholinergic receptors are the receptors that activate by the neurotransmitter acetylcholine. Nicotinic and muscarinic receptors are the two types of cholinergic receptors. The agonist nicotine stimulates nicotinic receptors, while muscarine stimulates the muscarinic receptors. Also, nicotinic receptors are inotropic ligand-gated, while muscarinic receptors are G-protein coupled. In addition, nicotinic receptors function within the central nervous system and at the neuromuscular junctions. In comparison, muscarinic receptors function in the central and peripheral nervous systems. Further, N1 and N2 are the types of nicotinic receptors, while M1, M2, M3, M4, and M5 are muscarinic receptors.
Figure 2: Nicotinic Receptors
Moreover, cholinergic receptors stimulate the ‘digest and rest’ response. It allows the flow of blood to less critical activities such as digestion. They respond to the neurotransmitter of the parasympathetic nervous system. They slow the heart rate and breathing, start the production of saliva, stimulate digestion, release waste and toxins, and allow lacrimation.
Similarities Between Adrenergic and Cholinergic Receptors
- Adrenergic and cholinergic receptors are two transmembrane receptors that bind to neurotransmitters.
- They respond to different parts of the autonomic nervous system, a part of the peripheral nervous system.
- They induce different effects on the body.
Difference Between Adrenergic and Cholinergic Receptors
Definition
Adrenergic receptors refer to receptors on the surface of cells that get activated when they bind a type of neurotransmitter called a catecholamine. In contrast, cholinergic receptors refer to receptors on the surface of cells that get activated when they bind a type of neurotransmitter called acetylcholine.
Part of the Nervous System
The sympathetic nervous system stimulates adrenergic receptors, while the parasympathetic nervous system stimulates cholinergic receptors.
Type of Neurotransmitter
Adrenergic receptors bind to catecholamines: epinephrine, and norepinephrine, while cholinergic receptors bind to acetylcholine.
Type of Receptor
Adrenergic receptors are G-protein coupled receptors, while cholinergic receptors are inotropic-ligand-gated and metabotropic receptors.
Structure
Adrenergic receptors are glycoproteins, while cholinergic receptors are integral membrane proteins.
Types
Adrenergic receptor types are alpha and beta receptors, while cholinergic receptor types are nicotinic and muscarinic.
Function
Adrenergic receptors stimulate the ‘fight or flight’ response, while cholinergic receptors stimulate the ‘digest and rest’ response.
Conclusion
In brief, adrenergic and cholinergic receptors are two types of transmembrane receptors. Catecholamines: epinephrine and norepinephrine in the sympathetic nervous system stimulate adrenergic receptors. Adrenergic receptors are glycoproteins that are G-protein coupled receptors. The two types of adrenergic receptors are alpha and beta receptors. They stimulate the ‘fight or flight’ response. In comparison, acetylcholine of the parasympathetic nervous system stimulates cholinergic receptors. Cholinergic receptors are integral membrane proteins that are inotropic-ligand gates and metabotropic receptors. Nicotinic and muscarinic receptors are the two types of cholinergic receptors. They stimulate the ‘digest and rest’ response. Therefore, the main difference between adrenergic and cholinergic receptors is their neurotransmitters.
References:
- Graham RM. Adrenergic receptors: structure and function. Cleve Clin J Med. 1990 Jul-Aug;57(5):481-91. doi: 10.3949/ccjm.57.5.481. PMID: 2164898.
- Carlson AB, Kraus GP. Physiology, Cholinergic Receptors. [Updated 2022 Aug 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
Image Courtesy:
- “Adrenoreceptor Signal Transduction” By en:User:Jpogi – Own work (CC-BY SA 4.0) via Commons Wikimedia
- “NAChR” By Nephron – Own Work (CC-BY SA 3.0) via Commons Wikimedia
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