The introduction of ion channel
When living cells continue to carry out metabolic activities, they must constantly exchange substances with the surrounding environment. The ion channels on the cell membrane are an important way to exchange such substances. It is known that most important substances to life are water-soluble, such as various ions, and sugars, they need to enter the cell, and the water-soluble waste generated in life activities also leaves the cell. The channel which they enter is the ion channel on the cell membrane. Ion channels are composed of special proteins produced by cells, and are gathered and embedded in the cell membrane, forming pores occupied by water molecules. These pores are the channels which water-soluble substances can enter and exit the cells quickly. The activity of the ion channel is that the cells regulate the entry and exit of the corresponding substance through the opening and closing of the ion channel, and are important for achieving various functions of the cell. Two German scientists, Erwin Nell and Bert zuckerman, won the 1991 Nobel Prize in physiology for their discovery of intracellular ion channels and pioneering of patch clamp techniques.
Ion channel classification
The opening and closing of the ion channel are called gating. According to the gating mechanism, the ion channels are divided into three categories: voltage gates, also known as voltage-dependent or voltage-sensitive ion channels, which are turned on and off due to changes in membrane potential, named after the ions that are most easily passed, such as K + , Na + , Ca 2 +, Cl-channel, and each type is divided into several subtypes; ligand gated, also known as chemical gated ion channel. It is opened by neurotransmitter binding to the binding sites on the protein receptor molecules of the channel, named after the neurotransmitter receptor, such as the acetylcholine receptor channel and the glutamate receptor channel. Non-selective cation channels are acted upon by a ligand. It is open and allows Na+, Ca2+ or K+ to pass through, which belongs to ligand gate family. Mechanogated, also known as mechanosensitive ion channel, is a kind of channel that senses the surface stress change of cell membrane and realizes the extracellular mechanical signal to intracellular transduction. The channel is divided into ion-selective and non-ion-selective channels, which is classified into tension-activated and tension-inactivated ion channels according to their functional effects. In addition, there are organelle ion channels, such as the voltage-dependent anion channel (VDAC), which is widely distributed on the outer membrane of mammalian cell mitochondria, located in the sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER) ryanodine receptor channel, IP3 receptor channel.
The role and research methods of ion channels
The main function of the ion channel is to increase the intracellular calcium concentration, which triggers a series of physiology such as muscle contraction, cell excitability, glandular secretion, Ca2+-dependent ion channel opening and closing, protein kinase activation and gene expression regulation; in excitatory cells such as nerves and muscles, Na+ and Ca2+ channels mainly regulate depolarization, and K+ mainly regulates repolarization and maintains resting potential, thereby determining cell excitability, refractoriness and conductivity. And ion channels can regulate vascular smooth muscle relaxation and contraction activities by K+, Ca2+, Cl-channel and some non-selective cation channels. It participates in synaptic transmission by K+, Na+, Ca2+, Cl-channel and some non-selective cation channels. In addition, ion channels maintain normal cell volume; in hypertonic environments, ion channel and transport system activation allows Na+, Cl-, organic solutions and water to enter the cell to regulate cell volume increase; in the osmotic environment, Na+, Cl-, organic solutions and water flow out of the cells to regulate cell volume reduction. The most direct way to study the function of ion channels is to directly measure the current or measurement changes in cell membrane potential through the ion channel using patch clamp technique. The patch-clamp technique uses a glass micropipette electrode to perform membrane or whole-cell potential monitoring, clamping, and membrane current recording. The molecular activity of the channel individual or population is analyzed by observing changes in membrane current. Biological technology provides a powerful tool for molecular structure analysis, gene cloning and functional expression of ion channels. For the gene encoding ion channel structure subunits, gene localization and cloning can be used to determine its localization on chromosomes, using reverse transcription-polymerase chain reaction, northern hybridization, etc., which define its distribution in organ tissues, and detect gene expression products by western hybridization. Fluorescence probe calcium image analysis technology provides an effective means for detecting intracellular free calcium ion concentration. Commonly used fluorescent probes are Fura-2/AM, Indo-1/AM, Fluo-3/AM, calcium Green, etc. Commonly used detection instruments include dual-wavelength micro-fluorescence photometer, laser scanning confocal microscope, etc. Currently, some new instruments have been produced, and they are a microscopic fluorescence device for measuring intracellular free calcium ions and fluorescence microscopy concentration detection system. The combination of ion concentration image recording and patch clamp recording, simultaneous photoelectric detection, image change and electrical signal changes, will obtain more ion channel function information.