What is the Difference Between Beta 1 and Beta 2 Receptors

The main difference between beta 1 and beta 2 receptors is that beta 1 receptors occur in the heart, kidney, and fat cells, whereas B2 receptors occur in the bronchioles of the lungs and arteries of the skeletal muscles. 

Beta 1 and beta 2 receptors are two adrenergic receptors responsible for signaling in the sympathetic nervous system.   

Key Areas Covered

1. What are Beta 1 Receptors
– Definition, Facts, Function
2. What are Beta 2 Receptors
– Definition, Facts, Function
3. Similarities Between Beta 1 and Beta 2 Receptors
– Outline of Common Features
4. Difference Between Beta 1 and Beta 2 Receptors
– Comparison of Key Differences

Key Terms 

Beta 1 Receptors, Beta 2 Receptors

What are Beta 1 Receptors

Beta 1 receptors are adrenergic receptors stimulated by the sympathetic nervous system. They predominantly occur in the heart, kidney, and fat cells. Also, they are glycoprotein-coupled receptors that communicate through Gs alpha subunits. The signaling of Gs initiates the cAMP-dependent pathway through Adenylyl cyclase. Also, the main function of beta 1 receptors is to increase heart rate and contractility. It increases the stroke volume and the cardiac output. In the kidney, beta 1 receptors contract the juxtaglomerular apparatus and release renin. It increases blood volume through the action of angiotensin II and aldosterone. In adipocytes, beta-1 receptors increase lipolysis.

Figure 1: Adrenergic Receptors

Furthermore, beta 1 receptors are an important part of the sympathetic nervous system. It prepares the body for the fight and flight response. When a person feels extreme fear or excitement, the body releases catecholamines such as epinephrine and norepinephrine. Beta 1 receptors increase heart rate and contractility. It allows the pumping of blood through the body faster. It allows the person to run faster and accomplish things for a short duration.

What are Beta 2 Receptors

Beta 2 receptors are the other type of beta-adrenergic receptors that occur in bronchioles and arteries of the skeletal muscles. Their function is the dilation of bronchioles and arteries. They are activated by catecholamines such as epinephrine and norepinephrine. Significantly, beta 2 adrenergic receptors are prototypical G-protein coupled receptors. Also, they occur in uterine muscles, cardiac muscles, mast cells, mucous glands, alveolar type II cells, vascular endothelium, epithelial cells, lymphocytes, eosinophils, and skeletal muscles.

Figure 2: Beta 2 Receptor

Moreover, beta 2 receptor agonists mimic epinephrine and norepinephrine. They reduce the adverse effects of these neurotransmitters. They are important in managing respiratory disorders such as chronic obstructive pulmonary disease (COPD) and asthma. In comparison, beta 2 receptor antagonists block the activation of beta 2 receptors. 

Similarities Between Beta 1 and Beta 2 Receptors

• Beat 1 and beta 2 receptors are two adrenergic receptors.
• They selectively bind catecholamines, norepinephrine, and epinephrine released by the sympathetic nervous system.
• They stimulate adenylate cyclase through trimeric Gs proteins.
• Beta-blockers are important in treating high blood pressure and asthma. 

Difference Between Beta 1 and Beta 2 Receptors

Definition

Beta 1 receptors refer to the receptors located in the heart and kidney, where they are involved in the regulation of heart rate, cardiac contractility, and plasma renin release, while beta 2 receptors refer to receptors that mediate relaxation of smooth muscle, including vascular beds, bronchus, intestine, and uterus.

Occurrence

Beta 1 receptors occur in the heart, kidney, and fat cells, while B2 receptors occur in the lungs’ bronchioles and arteries of the skeletal muscles. 

Function

Beta 1 receptors increase the heart rate and the strength of contraction, while beta 2 receptors increase the diameter of bronchioles and dilate vessels of the skeletal muscles. 

Agonist

Agonists for beta 1 receptors are dobutamine, while agonists for beta 2 receptors are salbutamol.

Antagonist

Antagonists of beta 1 receptors include metoprolol and atenolol, while antagonists of beta 2 receptors include alpha-methyl propranolol.

Conclusion

In brief, beta 1 and 2 receptors are two adrenergic receptors responding to the sympathetic nervous system. Beta 1 receptors occur in the heart, kidney, and fat cells. They are responsible for increasing heart rate and strength of the contraction. In comparison, beta 2 receptors occur in bronchioles and arteries of skeletal muscles. They increase the diameter of bronchioles and arteries in skeletal muscles. Therefore, the main difference between beta 1 and beta 2 receptors is their occurrence and function. 

References:

1. Alhayek S, Preuss CV. Beta 1 Receptors. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
2. Abosamak NER, Shahin MH. Beta2 Receptor Agonists and Antagonists. [Updated 2023 Feb 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Image Courtesy:

1. “Adrenoreceptor Signal Transduction” By TheCenci786 – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “2RH1” By Boghog at English Wikipedia – Own Work (Public Domain) via Commons Wikimedia