What is the Difference Between GABA A and GABA B Receptors

The main difference between GABA A and GABA B receptors is that GABA A receptors are ligand-gated chloride channels that mediate fast inhibitory signals, whereas GABA B receptors are G-protein coupled receptors that mediate slow inhibitory signals.

GABA A and GABA B receptors are two receptors that GABA uses to prevent hyperexcitation. GABA is an inhibitory neurotransmitter. 

Key Areas Covered

1. What are GABA A Receptors
– Definition, Facts, Importance
2. What are GABA B Receptors
– Definition, Facts, Importance
3. Similarities Between GABA A and GABA B Receptors
– Outline of Common Features
4. Difference Between GABA A and GABA B Receptors
– Comparison of Key Differences

Key Terms 

GABA A Receptors, GABA B Receptors 

What is GABA A Receptors

GABA A receptors are ionotropic receptors that are ligand-gated ion channels. γ-aminobutyric acid (GABA) is the endogenous ligand of the GABA A receptor. It is the major inhibitory neurotransmitter of the central nervous system. GABA A receptor in the postsynaptic cell is selectively permeable to chloride (Cl-) ions. It is also permeable to bicarbonate ions (HCO₃^–). When the membrane potential exceeds the equilibrium potential, chloride ions flow into the cell. It causes an inhibitory effect on generating an action potential by the membrane of the postsynaptic cell. It is called the inhibitory postsynaptic potential (IPSP), which is -100 mV.

Figure 1: GABA A Receptor

Furthermore, the active site of the GABA A receptor binds to the GABA. It also binds to several drugs, including muscimol, gaboxadol, and bicuculline. In addition, the receptor contains allosteric binding sites for the indirect regulation of the activity of the receptor. Nonbenzodiazepines, benzodiazepines, neuroactive steroids, alcohol (ethanol), barbiturates, inhaled anesthetics, kavalactones, cicutoxin, and picrotoxin are some drugs that bind to the allosteric binding sites of the GABA A receptor. 

What are GABA B Receptors

GABA B receptors are another receptor for gamma-aminobutyric acid (GABA). However, they are metabotropic receptors linked to G-protein and potassium ions (K+). GABA B receptors occur in the central nervous system and peripheral nervous system. At the end of the action potential, the changing potassium concentrations hyperpolarize the neuron. GABA B hyperpolarization potential is higher than the GABA A hyperpolarization potential. Also, GABA B receptor Inhibitory postsynaptic potential (IPSP) is -100 mV.

Figure 2: GABA B Receptor

Moreover, GABA B receptors are G-protein coupled receptors that mediate the opening of the potassium ion channels, which brings the neuron into the equilibrium potential after an action potential. It also reduces the frequency of action potential, reducing the release of neurotransmitters. Therefore, similar to GABA A receptors, GABA B receptors generate inhibitory actions.  

Similarities Between GABA A and GABA B Receptors

• GABA A and GABA B receptors are two GABA receptors.
• They are responsible for preventing hyperexcitation. 

Difference Between GABA A and GABA B Receptors

Definition

GABA A receptors refer to an ionotropic receptor and ligand-gated ion channel. In contrast, GABA B receptors refer to G-protein coupled receptors for gamma-aminobutyric acid (GABA), making them metabotropic receptors. 

Type of Receptor

GABA A receptors are ionotropic receptors, while GABA B receptors are metabotropic receptors. 

Location

GABA A receptors are postsynaptic, while GABA B receptors are both pre-and postsynaptic. 

Structure

GABA A receptors are pentamers, while GABA B receptors are dimers.  

Importance

GABA A receptors are ligand-gated chloride channels that mediate fast inhibitory signals, while GABA B receptors are G-protein coupled receptors that mediate slow inhibitory signals.

Mechanism of Action

GABA A receptors undergo postsynaptic inhibition by increasing chloride ion influx, while GABA B receptors undergo presynaptic inhibition by decreasing calcium ion entry and postsynaptic inhibition by increasing potassium ion entry.  

Conclusion

In brief, GABA A and GABA B receptors are two GABA receptors responsible for preventing hyperexcitation. GABA A receptors are postsynaptic ionotropic receptors. They are pentamers. Also, they are ligand-gated chloride channels that mediate fast inhibitory signals. They increase chloride ion influx for postsynaptic inhibition. In comparison, GABA B receptors are metabotropic receptors that undergo pre- and postsynaptic inhibition. They are dimers. Also, they are G-protein coupled receptors mediating slow inhibition. They decrease calcium ion influx in the presynaptic inhibition and increase potassium ion entry in the postsynaptic inhibition. Therefore, the main difference between GABA A and GABA B receptors is their mechanism of action.   

References:

1. Terunuma M. Diversity of structure and function of GABA_Breceptors: a complexity of GABA_B-mediated signaling. Proc Jpn Acad Ser B Phys Biol Sci. 2018;94(10):390-411. doi: 10.2183/pjab.94.026. PMID: 30541966; PMCID: PMC6374141.

Image Courtesy:

1. “Fig-GABAA receptor” By Swastik.phulera – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “6VJM GABAB Receptor dimer inactive.” By C22H31NO2 – Own Work (CC-BY SA 4.0) via Commons Wikimedia