Difference Between Ion Channel and Transporter

Main Difference – Ion Channel and Transporter

Ion channel and transporter are two types of transmembrane proteins that control the movement of ions across the cell membrane. Both ion channel and transporter aid the selectively permeable nature of the cell membrane by allowing only the selected molecules to pass through the cell membrane. The main difference between ion channel and transporter is that the movement of ions occurs through a concentration or electrochemical gradient in ion channels whereas the movement of ions occurs against the concentration gradient in transporters. Transporters are also called ion pumps. Ion channels are fast transporters while transporters make slow translocations.

Key Areas Covered

1. What is an Ion Channel
– Definition, Facts, Type of Transportation
2. What is a Transporter
– Definition, Facts, Type of Transportation
3. What are the Similarities Between Ion Channel and Transporter
– Outline of Common Features
4. What is the Difference Between Ion Channel and Transporter
– Comparison of Key Differences

Key Terms: ATP, Concentration Gradient, Electrochemical Gradient, Ion Channel, Transmembrane Proteins, Transporter

What is Ion Channel

Ion channels refer to the pore-forming membrane proteins that allow the movement of ions through the cell membrane. They are either voltage-gated or ligand-gated. Some channels open and close in response to mechanical signals as well. Ion channels are a type of transmembrane proteins with multimeric subunits. Upon opening, specific ions can flow through the ion channel through either a concentration or electrochemical gradient. The diameter of the ion that is going to pass through the ion channel will be a selective factor for the transportation. The structure of an ion channel is shown in figure 1.

Main Difference - Ion Channel vs Transporter

Figure 1: Ion Channel
Channel domain, 2. Outer vestibule, 3. Selectivity filter, 4. Diameter of the selectivity filter, 5. Phosphorylation site, 6. Cell membrane

Ion channels play an important role in excitatory cells such as muscle cells and nerve cells. They are involved in the transmission of nerve signals on the nerve cell membrane. Ion channels can also be closed quickly to enter into a resting state. As the movement of ions occurs through a gradient, the cell need not invest energy in the movement of ions. Hence, ion channels are a passive method of transportation of ions. Sodium and potassium ion channels are examples of ion channels.

What is a Transporter

Transporter refers to a transmembrane protein that transports ions across the cell membrane against the concentration gradient by active transport. Hence, transporters consume energy in the form of ATP for the movement of ions. In other words, with the use of energy, transporters can move ions thermodynamically uphill to a higher energy state. A transporter can be either a primary pump and a secondary pump. The primary pumps hydrolyze ATP. With hydrolyzation, the conformation of the transporter changes and become capable of translocating the previously-bound specific ions, releasing them in or out of the cell. Sodium-potassium ATPase is an example of a primary transporter and it is shown in figure 2.

Difference Between Ion Channel and Transporter

Figure 2: Sodium-Potassium ATPase

The regulation of transporters is achieved by the internal concentration of ions. The secondary pumps transport ions. They are capable of transporting two different types of ions: one ion is transported along its gradient and the other is transported against the gradient. The movement of the first ion serves as the energy source in the movement of the second ion. Symporters and antiporters are the two types of transporters. In symporters, each type of ions moves in the same direction across the membrane. In antiporters, the two types of ions move in the opposite direction across the membrane. Sodium-potassium-chloride symporter is an example of a secondary transporter.

Similarities Between Ion Channel and Transporter

Ion channel and transporter are two types of transmembrane proteins involved in the movement of ions across the cell membrane.
Both ion channel and transporter are important in maintaining the homeostasis of the cytoplasm.

Definition

Ion Channel: Ion channels are pore-forming membrane proteins that allow the movement of ions through the cell membrane.

Transporter: Transporters are transmembrane proteins that transport ions across the cell membrane against the concentration gradient.

Gradient

Ion Channel: Ion channels transport ions through the concentration or electrochemical gradient.

Transporter: Ions move across the cell membrane against the gradient in transporters.

Energy

Ion Channel: Ion channels do not use cellular energy for the transportation of ions. Hence, it is a passive transport mechanism.

Transporter: Transporters use cellular energy in the form of ATP. Hence, it is an active transport mechanism.

Types

Ion Channel: Voltage-gated ion channels, ligand-gated ion channels, and aquaporins are the three types of ion channels.

Transporter: Primary transporters, symporters, and antiporters are the three types of transporters.

Conclusion

Ion channels and transporters are two types of transmembrane proteins involved in the movement of ions across the cell membrane. Ion channels transport ions through a concentration or electrochemical gradient. However, transporters are involved in the movement of ions against the gradient. Therefore, transporters require energy in the form of ATP for the transportation of ions. The main difference between ion channels and transporters is the use of energy for the transportation of each type of transmembrane protein.

Reference:

1. Gadsby, David C. “Ion channels versus ion pumps: the principal difference, in principle.” Nature reviews. Molecular cell biology, U.S. National Library of Medicine, May 2009, Available here.

Image Courtesy:

1. “Ion channel” By Original uploader was Outslider (Paweł Tokarz) at pl.wikipedia – Transferred from pl.wikipedia to Commons by Masur using CommonsHelper (Public Domain) via Commons Wikimedia
2. “Scheme sodium-potassium pump-en” By LadyofHats Mariana Ruiz Villarreal – Own work (Public Domain) via Commons Wikimedia