What is the Difference Between Ion Pumps and Gated Channels

The main difference between ion pumps and gated channels is that ion pumps undergo active transport of ions against a concentration gradient, whereas gated channels allow the passive diffusion of ions down a concentration gradient. 

Ion pumps and gated channels are the two transmembrane proteins that transport ions. They occur on the cell membrane. 

Key Areas Covered

1. What are Ion Pumps
– Definition, Types, Importance
2. What are Gated Channels
– Definition, Types, Importance
3. Similarities Between Ion Pumps and Gated Channels
– Outline of Common Features
4. Difference Between Ion Pumps and Gated Channels
– Comparison of Key Differences

Key Terms 

Gated Channels, Ion Pumps, Primary Transporter, Secondary Transporter

What are Ion Pumps

Ion pumps or active transporters are transmembrane proteins that move ions across a biological membrane. Also, it occurs against a concentration gradient by using energy. It is important for most cellular processes, including cellular communication, energy production, and maintaining homeostasis. The transportation energy comes from either ATP, sunlight, and redox reactions. There are two types of ion pumps: primary transporter and secondary transporter. 

Primary Transporter 

Primary transporter uses ATP as the energy to transport ions across the membrane. There are two types of primary transporters: active transporters and ATP-producing transporters. The active transporter transports ions from low to high concentrations using ATP energy. Examples are P-type ATPases Na +, K+, and Ca2+ ions by phosphorylation. Na+/K+-ATPase is a P-type ATPase transporter. Another example of an active transporter is A-type ATPases that transport anions and ABC transporters.

Figure 1: Sodium-Potassium Pump

Furthermore, the ATP-producing transporter is opposite to the active transporter, moving ions from high to low concentration, producing ATP. Therefore, the concentration gradient is used to produce energy in the form of TAP in the ATP-producing transporter. ATP synthase in the electron transport chain of oxidative phosphorylation is an example of an ATP-producing transporter.

Secondary Transporter

Secondary transporters transport ions and small molecules from low to high concentration against the concentration gradient. Importantly, potential energy from the concentration gradient is used as the energy for the transport of ions in the secondary transporter. Sodium-dependent glucose transporter is an example of a secondary transporter. It occurs in the intestine and kidney. The sodium-potassium pump maintains the sodium gradient. When sodium flows down, the concentration gradient is used as the potential energy to transport glucose into the cell. Also, it is a uniporter. The other types of secondary transporters include symporters and antiporters. Both sodium and glucose molecules are transported in the same direction in symporters, while they are transported in opposite directions in antiporters. 

What are Gated Channels

Gated channels are another type of transmembrane proteins that transport ions. There are three types of gated channels: voltage-gated, ligand-gated, and mechano-sensitive ion channels.

Voltage-Gated Ion Channels

Voltage-gated ion channels include Na+, K+, Ca2+, and Cl- channels. Of these, voltage-gated Na+ channels are responsible for generating action potentials. Meanwhile, voltage-gated Ca2+ channels maintain the calcium concentration inside the cell. At the same time, voltage-gated K+ channels maintain the resting membrane potential. Further, voltage-gated Cl- channels maintain excitability and cell volume. 

Ligand-Gated Ion Channels (LGICs)

Ligand-gated Ion channels are targets for drugs, and there are three types of them: ‘cys-looped’ ligand-gated ion channels, ionotropic glutamate receptors, and P2X receptors. Nicotinic acetylcholine receptors (nAChR), γ-aminobutyric acid (GABA) receptors, 5-hydroxytryptamine-3 (5HT3) receptors, and glycine receptors are examples of LGICs. The nAChR and 5HT3 receptors are excitatory, while GABA and glycine receptors are inhibitory. Also, glutamate is the neurotransmitter that activates the ionotropic glutamate receptors. The α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, kainate receptors, and N-methyl-D-aspartate (NMDA) receptors are examples of ionotropic glutamate receptors. Additionally, P2X receptors are Na+, K+, and Ca2+ ion channels activated by ATP.

Figure 2: Mechanically-Gated Channels

Mechano-Sensitive Ion Channels

The mechano-sensitive ion channels respond to the changes in the mechanical forces. They regulate blood pressure, stimulate muscle and bone development, and sense hearing and touch. They also involve in cardiac arrhythmias, muscular dystrophy, neuronal degeneration, polycystic kidney disease, and tumor metastasis.

Similarities Between Ion Pumps and Gated Channels

• Ion pumps and gated channels are transmembrane proteins on the plasma membrane.
• They transport ions across the membrane. 

Difference Between Ion Pumps and Gated Channels

Definition

Ion pumps refer to a membranal complex of proteins capable of transporting ions against a concentration Gradient using the energy from ATP. In contrast, gated channels refer to a class of transmembrane proteins that form ion channels that are activated by changes in the electrical membrane potential. 

Mechanism of Transport

Ion pumps undergo active transport of ions against a concentration gradient, while gated channels allow the passive diffusion of ions down a concentration gradient. 

Types

Two types of ion pumps occur, primary and secondary transporters, while three types of gated channels occur: voltage-gated, ligand-gated, and mechano-sensitive ion channels.

Examples

Ion pumps include Na+, K+-ATPase, Ca2+-ATPase, H+-ATPase, and H+, K+-ATPase while gated channels include voltage-gated channels include those selectively permeable to Na+, Ca2+, K+, and Cl-. 

Conclusion

In brief, ion pumps and gated channels are two transmembrane proteins that occur on the surface of the plasma membrane. Ion pumps undergo active transport of ions against a concentration gradient. They include Na+, K+-ATPase, Ca2+-ATPase, H+-ATPase, and H+, K+-ATPase. In comparison, gated channels undergo passive diffusion of ions down a concentration gradient. They include voltage-gated channels selectively permeable to Na+, Ca2+, K+, and Cl-. Therefore, the main difference between ion pumps and gated channels is the transport mechanism. 

References:

1. Wikimedia Foundation. (2023r, May 17). Ion Transporter. Wikipedia. 
2. Ratan-NM. (2018, October 26). Types of ion channels in the body. News. 

Image Courtesy:

1. “Sodium-Potassium Pump” By Lrobsss – Own work (CC-BY-SA 4.0) via Commons Wikimedia
2. “1217 Mechanically-gated Channels-02” By OpenStax – Own Work (CC-BY 4.0) via Commons Wikimedia