An integral membrane protein which contains a pore through which ions, water, or polar molecules permeate. For any given channel, the pore is usually very selective for the particular ion or molecule. For example, sodium (Na⁺) channels are very selective for Na⁺ over other cations.

The channel pore may be constitutively open, or it may be gated to the open state by various stimuli such as chemical ligands, voltage, temperature, or mechanical stimulation of the membrane.

Proposed model for the inactivation of some voltage-gated ion channels. According to this model, after channel opening, the pore of the open channel is plugged by a globular cytoplasmic portion of the channel protein. The globular portion (ball of amino acids) is tethered to the rest of the protein by a linker part (chain of amino acids).

Channel inactivation

Neuronal Action Potential - Important Features of the Neuronal Action Potential

The Hodgkin cycle represents a positive feedback loop in neurons, where an initial membrane depolarization from the resting value (∼ −70 mV) to the threshold value (∼ −50 mV) leads to rapid depolarization of the membrane potential to approach the equilibrium potential for Na⁺ (V_Na ≈ +60 mV). The voltage-gated Na⁺ channels of neurons are responsible for the Hodgkin cycle.

See the figure depicting the Hodgkin cycle.

Important Features of the Neuronal Action Potential

Lidocaine is a local anesthetic and an antiarrhythmic drug. It is a commonly used local anesthetic for minor surgery and in dental procedures. Lidocaine is also used topically to relieve itching, burning, and pain from skin inflammations.

Lidocaine's mechanism of action is to block fast voltage-gated Na⁺ channels of neurons and cardiac myocytes.

Other names used for lidocaine are xylocaine and lignocaine.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

Lidocaine (Wikipedia)

Neurotoxins are chemical molecules that have an adverse effect on neuron function and, thus, disrupt the normal function of the nervous system. Neurotoxins could be small molecules or peptides and can be derived from a variety of invertebrate and vertebrate animals, as well as plant species.

The following is a short list of some examples of neurotoxins:

α-Bungarotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

Chlorotoxin: A peptide neurotoxin that inhibits chloride channels.

α-Conotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.

δ-Conotoxin: A peptide neurotoxin that inhibits voltage-gated sodium channels.

w-Conotoxin: A peptide neurotoxin that inhibits N-type voltage-gated calcium channels.

Picrotoxin: Inhibits GABA_A receptor chloride channels.

Tetrodotoxin: Inhibitor of neuronal voltage-gated sodium channels.

A local topical anesthetic.

Procaine's mechanism of action is to block fast voltage-gated Na⁺ channels of neurons.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

Procaine (Wikipedia)

TEA

An inhibitor of voltage-gated potassium (K⁺) channels.

TEA is a quaternary ammonium cation (positively charged ion). It is also commonly used as a cation replacement for sodium (Na⁺) in physiological buffers used in ion replacement experiments.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

TTX

Inhibitor of fast voltage-gated sodium (Na⁺) channels of neurons and muscle cells. It is an extremely potent and toxic neurotoxin.

Pharmacological Inhibition of Na⁺ and K⁺ Channels

Tetrodotoxin (Wikipedia)

The membrane voltage that must be reached in an excitable cell (e.g., neuron or muscle cell) during a depolarization in order to generate an action potential. At the threshold voltage, voltage-gated channels become activated. Threshold is approximately −50 to −40 mV in most excitable cells.

Sub-threshold
Supra-threshold

Neuronal Action Potential - Introduction