An ion channel is a tansmembrane protein that forms a pore in the membrane and allows ions to pass through it. Ions are electrically charged particles; they can be postitive but also negatively charged. They are in constant exchange between the cell and its environment or another neighboring cell.
What is an ion channel?
The membrane of a cell consists of a lipid bilayer. Ion channels are transmembrane proteins that span the membrane and allow ions to pass through. Ion channels are also called channel proteins because they form a passageway. The group of ion channels is divided into different categories, the active ion channels and the passive ion channels. The active ion channels create the passage of ions by active transport thus require energy for this process. The passive ion channels, on the other hand, do not consume energy and allow the passage of ions along a pre-existing eletrochemical gradient. This gradient can be divided into the chemical and the electrochemical components. The chemical gradient describes a concentration gradient. The particles of a certain substance, such as potassium, move uncoordinated between two compartments with the help of ion channels. This results in a uniform distribution of these particles between the two compartments. This is also referred to as Brownian molecular motion. The electrical gradient, on the other hand, involves the distribution of electrical voltage. For example, if there is an increased negative charge in one compartment, an electrical gradient is formed. The positive particles of the other compartment then move to the negatively charged compartment to rebalance the unequal voltage built up by the gradient. The active ion channels specifically work against a gradient. For example, they may transport additional negatively charged particles into the already negatively charged compartment. However, this process requires an expenditure of energy.
Function, action, and tasks
Ion channels have a variety of functions. Transmitter-gated ion channels of the synapses of neurons have an important function in the transmission of signals between different neurons. These types of ion channels are located at the postsynaptic terminal. When an incoming signal occurs, the synapse releases a specific neurotransmitter. The transmitter enters the synaptic cleft and binds to the receptors of the transmitter-gated ion channels. These are opened and the membrane potential of the postsynapse is changed. Depending on this, an excitatory or inhibitory membrane potential is produced. This depends on whether the membrane potential is raised or lowered and this in turn is determined by the influx of ions through the transmitter-gated ion channel. The transmission of stimuli in the neuron, this can be in the brain or also in the spinal cord, is generated by ion channels. For example, the process of vision is made possible in this way, but also the transmission of stimuli in a reflex such as the hamstring reflex. When a change in membrane potential occurs, the opening of ion channels along neurons occurs. This creates conduction of the altered membrane potential enltang a neuron similar to a domino effect. The membrane voltage initially comes about because there is a negative charge inside the neuron and a positive charge in the extracellular area. If the so-called resting potential of the membrane voltage is exceeded, hyperpolarization of the membrane occurs. As a result, membrane voltage becomes even more negative. This happens due to the opening or also closing of the ion channels. These ion channels are potassium, calcium, chloride and sodium channels. They are voltage-dependent, i.e. they open or close depending on the membrane potential. This process is called action potential and is divided into different steps. First, the initiation phase occurs. Then there is depolarization followed by repolarization, in which the resting potential is reached again. Usually, however, hyperpolarization occurs before repolarization. This serves to ensure that no further action potential is triggered directly after the action potential that has occurred and that a continuous stimulus occurs.Ion channels also possess an important function in the regulation of osmosis as well as in the maintenance of acid-base balance in the body.
Formation, occurrence, properties, and optimal values
As mentioned earlier, there are active and passive ion channels. However, they can also be distinguished based on the nature of their steruerization. These are voltage-gated ion channels that serve for stimulus transmission in neurons. They can also be ligand-gated, such as the transmitter-gated ion channels of the synapses for relaying signals to other neurons or also for signal transmission to the muscles. Other ion channels are the mechanosensitive channels. They are regulated by mechanical stimuli such as pressure. Temperature-gated ion channels are opened or closed when a certain threshold of a temperature is reached. And light-gated ion channels are regulated by a specific wavelength of light. An example of this is rhodopsin, which is bound to a channel and regulates it. These occur in the eye, for example, and are integral to the visual process.
Diseases and disorders
Ion channels can be affected by some diseases. One besipiel is a defective calcium channel in the cerebellum. This defect is a trigger for epilepsy. Another example is Lambert-Eaton syndrome. In this case, patients form antibodies against the calcium channels of the neuromuscular end plate. This is the area of stimulus transmission between neurons and the musculature. Signals are weakened and muscle weakness results. Men tend to be more affected by this condition than women.
