Ion channels are membrane proteins, which play a principal role in regulating cellular excitability. They are found in virtually all cells, and are of crucial physiological importance. Based on the stimulus to which they respond, ion channels are divided into three superfamilies
Ion channels are membrane proteins, which play a principal role in regulating cellular excitability. They are found in virtually all cells, and are of crucial physiological importance. Based on the stimulus to which they respond, ion channels are divided into three superfamilies: voltage-gated, ligand-gated and mechano-sensitive ion channels.
Voltage-Gated Ion Channels
Voltage-gated channels respond to perturbations in cell membrane potential, and are highly selective for a specific ion, i.e., Na+, K+, Ca2+, and Cl-. They are further subdivided into families based on the major permeant ion.
- Voltage-gated Na+ channel – These channels are responsible for the generation of action potentials of long duration, and thus are targets of local anesthetics, such as lidocaine and benzocaine.
- Voltage-gated Ca2+ channels – They regulate intracellular Ca2+ concentrations, and thus are responsible for a wide range of biochemical processes within cells. One of the most important processes regulated by these channels is the release of neurotransmitters at synapses. Calcium channel blockers are valuable in treating a variety of conditions ranging from heart disease to anxiety disorders.
- Voltage-gated K+ channels – They constitute the largest and the most diverse class of voltage-gated ion channels. They are imperative in generating the resting membrane potential.
- Voltage-gated Cl- channels – These channels are present in every type of neuron and are involved in regulating excitability and cell volume. They are also known to contribute to the resting membrane potential.
Ligand-Gated Ion Channels (LGIC)
LGIC are targets for many drugs, such as anesthetics, antipsychotics, and antidepressants. They are named according to the ligand to which they respond and are divided into three families based upon molecular biology and protein structure criteria.
They constitute the largest class of LGICs and include nicotinic acetylcholine receptors (nAChR), γ-aminobutyric acid (GABA) receptors, 5-hydroxytryptamine-3 (5HT3) receptors, and glycine receptors. The nAChR and 5-HT3R are excitatory receptors, while the GABA receptors and glycine receptors are inhibitory in nature.
The nAChRs are activated endogenously by the neurotransmitter acetylcholine. Acetylcholine plays an important role in various cognitive processes, such as learning, memory, and attention. It is also an important signaling che