The key difference between voltage gated sodium and potassium channels is that voltage gated sodium channels have two gates named inactivation gate and activation gate, while voltage gated potassium channels have only one gate.
Voltage gated channels are a type of gated channel that is normally found closed. They open in response to a change in the membrane potential. They can also change their configuration and ion permeability. Sodium and Potassium voltage gated channels are two types of voltage gated channels mainly found in the axon hillock of nerve cells. They are also found in muscle fibers. Their primary function is to generate and propagate the action potential. Sodium channels have two gates, while potassium channels have a single gate.
CONTENTS
1. Overview and Key Difference
2. What are Voltage Gated Sodium Channels
3. What are Voltage Gated Potassium Channels
4. Similarities – Voltage Gated Sodium and Potassium Channels
5. Voltage Gated Sodium vs Potassium Channels in Tabular Form
6. Summary – Voltage Gated Sodium vs Potassium Channels
What are Voltage Gated Sodium Channels?
Voltage gated sodium channels are a type of voltage gated channels found in nerve cells that facilitate transmembrane transport of Na+. In fact, they serve as the most important ion channels in neurons. Voltage gated sodium channels were discovered by Hodgkin and Huxley in 1952. In mammals, at least ten genes are involved in encoding these channels. They are responsible for the resting potential and initiation and propagation of action potential in neurons and muscle fibers. There are at least nine distinct sodium channel isoforms in the nervous system. Structurally, they are transmembrane proteins composed of four highly homologous transmembrane domains (each domain contains six transmembrane helical segments), three intracellular loops, N-terminus and C-terminus. The α subunit is the core subunit that is pore-forming.
Figure 01: Voltage Gated Sodium Channels
Moreover, sodium channels have two gates. These two gates are the inactivation gate and the activation gate. They exist in three primary states in the axon hillock. The three states are closed resting state, open conducting state, and nonconducting inactivated state. In the resting phase, sodium ion concentration is higher in the exterior of neuron cells. Sodium channels become activated when the cell membrane depolarizes by a few millivolts. Sodium ion influx occurs through sodium channels, and it causes further depolarization of the cell membrane. As a result, the rising phase of the action potential is initiated. The creation of action potential occurs due to depolarization and then is transformed into a response like releasing neurotransmitters propagating the action potential in one direction. Within a few seconds, sodium channels become closed, preventing the further influx of sodium ions.
The activity of voltage gated sodium channels is highly important in relation to neuron excitability. Hence, they can be linked to neurological disorders such as epilepsy (a brain dysfunction syndrome that is also known as ion channel disease) and pain (an acute or chronic disease), which are related to neuron excitability. Moreover, many other neurological diseases are prone to occur due to the mutations in or dysfunctions of α subunits or β-subunits of sodium voltage gated channels.
What are Voltage Gated Potassium Channels?
Votage gated potassium channels are transmembrane proteins embedded in the membrane of neurons and muscle fibers. Potassium channels are highly selective. They are found in all living organisms. These channels are responsible for the potassium ion efflux in the neurons in order to return the depolarized cell to a resting state after a nerve impulse. Hence they are considered “brakes” on the sensory system. When the membrane depolarizes, potassium channels are opened, and the efflux of potassium ion occurs. This causes repolarization. Potassium ions are slow to be closed. Hence, further potassium ion movement occurs, making the membrane hyperpolarized.
Figure 02: Voltage Gated Potassium Channels
Structurally, potassium channels have four subunits. However, unlike the voltage gated sodium channels, potassium channels lack an inactivation gate. Therefore, potassium channels have a single gate.
What are the Similarities Between Voltage Gated Sodium and Potassium Channels?
- Voltage gated sodium and potassium channels are two gated ion channels found in all living organisms.
- They are proteins embedded in cell membranes.
- They are members of a single superfamily of voltage-gated cation channels.
- Both play important roles in the generation and propagation of action potential along the neurons.
- They have four subunits.
- Moreover, they have pore-forming domains and voltage-sensitive domains.
- Both channels are therapeutic targets.
- They are selective for their ions.
What is the Difference Between Voltage Gated Sodium and Potassium Channels?
The key difference between voltage gated sodium and potassium channels is that there are two gates in voltage gated sodium channels, while there is a single gate in voltage gated potassium channels. Moreover, the major role of voltage gated sodium channels is the depolarization of the membrane during the action potential, while the major role of voltage gated potassium channels is the repolarization of the membrane.
The below infographic presents the differences between voltage gated sodium and potassium channels in tabular form for side-by-side comparison.
Summary – Voltage Gated Sodium vs Potassium Channels
Voltage gated sodium and potassium channels are fundamental to the generation of action potentials in excitable cells such as neurons and muscle fibers. They are transmembrane proteins having pore-forming and voltage-sensing units. Sodium voltage gated channels have two gates, while potassium voltage gated channels have only one gate. Sodium channels facilitate the movement of sodium ions from the exterior to the interior, causing the depolarization of the membrane. In contrast, potassium channels facilitate the movement of potassium ions from interior to exterior, causing the repolarization of the membrane. So, this summarizes the difference between voltage gated sodium and potassium channels.
Reference:
1. Wang, Jun, et al. “Distribution and Function of Voltage-Gated Sodium Channels in the Nervous System.” Channels (Austin, Tex.), Taylor & Francis, 2 Nov. 2017.
2. Kim, Dorothy M, and Crina M Nimigean. “Voltage-Gated Potassium Channels: A Structural Examination of Selectivity and Gating.” Cold Spring Harbor Perspectives in Biology, Cold Spring Harbor Laboratory Press.
Image Courtesy:
1. “Sodium inactivation mechanism” By Clara fcn (talk) 17:11, 25 March 2015 (UTC) – Own work (After Goldin, 2003) (CC BY-SA 3.0) via Commons Wikimedia
2. “Voltage-gated Ion Channel” By Tlunchman – Own work (CC BY-SA 4.0) via Commons Wikimedia