Diversity Ion channel

1 diversity

1.1 classification gating

1.1.1 voltage-gated
1.1.2 ligand-gated
1.1.3 other gating


1.2 classification type of ions
1.3 classification cellular localization
1.4 other classifications

diversity

there on 300 types of ion channels in cells of inner ear. ion channels may classified nature of gating, species of ions passing through gates, number of gates (pores) , localization of proteins.

further heterogeneity of ion channels arises when channels different constitutive subunits give rise specific kind of current. absence or mutation of 1 or more of contributing types of channel subunits can result in loss of function and, potentially, underlie neurologic diseases.

classification gating

ion channels may classified gating, i.e. opens , closes channels. voltage-gated ion channels open or close depending on voltage gradient across plasma membrane, while ligand-gated ion channels open or close depending on binding of ligands channel.

voltage-gated

voltage-gated ion channels open , close in response membrane potential.

voltage-gated sodium channels: family contains @ least 9 members , largely responsible action potential creation , propagation. pore-forming α subunits large (up 4,000 amino acids) , consist of 4 homologous repeat domains (i-iv) each comprising 6 transmembrane segments (s1-s6) total of 24 transmembrane segments. members of family coassemble auxiliary β subunits, each spanning membrane once. both α , β subunits extensively glycosylated.
voltage-gated calcium channels: family contains 10 members, though these members known coassemble α2δ, β, , γ subunits. these channels play important role in both linking muscle excitation contraction neuronal excitation transmitter release. α subunits have overall structural resemblance of sodium channels , equally large.

cation channels of sperm: small family of channels, referred catsper channels, related two-pore channels , distantly related trp channels.


voltage-gated potassium channels (kv): family contains 40 members, further divided 12 subfamilies. these channels known role in repolarizing cell membrane following action potentials. α subunits have 6 transmembrane segments, homologous single domain of sodium channels. correspondingly, assemble tetramers produce functioning channel.
some transient receptor potential channels: group of channels, referred trp channels, named after role in drosophila phototransduction. family, containing @ least 28 members, incredibly diverse in method of activation. trp channels seem constitutively open, while others gated voltage, intracellular ca, ph, redox state, osmolarity, , mechanical stretch. these channels vary according ion(s) pass, being selective ca while others less selective, acting cation channels. family subdivided 6 subfamilies based on homology: classical (trpc), vanilloid receptors (trpv), melastatin (trpm), polycystins (trpp), mucolipins (trpml), , ankyrin transmembrane protein 1 (trpa).
hyperpolarization-activated cyclic nucleotide-gated channels: opening of these channels due hyperpolarization rather depolarization required other cyclic nucleotide-gated channels. these channels sensitive cyclic nucleotides camp , cgmp, alter voltage sensitivity of channel’s opening. these channels permeable monovalent cations k , na. there 4 members of family, of form tetramers of six-transmembrane α subunits. these channels open under hyperpolarizing conditions, function pacemaking channels in heart, particularly sa node.
voltage-gated proton channels: voltage-gated proton channels open depolarization, in ph-sensitive manner. result these channels open when electrochemical gradient outward, such opening allow protons leave cells. function appears acid extrusion cells. important function occurs in phagocytes (e.g. eosinophils, neutrophils, macrophages) during respiratory burst. when bacteria or other microbes engulfed phagocytes, enzyme nadph oxidase assembles in membrane , begins produce reactive oxygen species (ros) kill bacteria. nadph oxidase electrogenic, moving electrons across membrane, , proton channels open allow proton flux balance electron movement electrically.

ligand-gated

also known ionotropic receptors, group of channels open in response specific ligand molecules binding extracellular domain of receptor protein. ligand binding causes conformational change in structure of channel protein leads opening of channel gate , subsequent ion flux across plasma membrane. examples of such channels include cation-permeable nicotinic acetylcholine receptor, ionotropic glutamate-gated receptors, acid sensing ion channels (asics), atp-gated p2x receptors, , anion-permeable γ-aminobutyric acid-gated gabaa receptor.

ion channels activated second messengers may categorized in group, although ligands , second messengers otherwise distinguished each other.

other gating

gating includes activation , inactivation second messengers inside of cell membrane – rather outside cell, in case ligands.

some potassium channels:

inward-rectifier potassium channels: these channels allow potassium ions flow cell in inwardly rectifying manner: potassium flows more efficiently out of cell. family composed of 15 official , 1 unofficial members , further subdivided 7 subfamilies based on homology. these channels affected intracellular atp, pip2, , g-protein βγ subunits. involved in important physiological processes such pacemaker activity in heart, insulin release, , potassium uptake in glial cells. contain 2 transmembrane segments, corresponding core pore-forming segments of kv , kca channels. α subunits form tetramers.
calcium-activated potassium channels: family of channels activated intracellular ca , contains 8 members.
two-pore-domain potassium channels: family of 15 members form known leak channels, , display goldman-hodgkin-katz (open) rectification.


light-gated channels channelrhodopsin directly opened photons.
mechanosensitive ion channels open under influence of stretch, pressure, shear, , displacement.
cyclic nucleotide-gated channels: superfamily of channels contains 2 families: cyclic nucleotide-gated (cng) channels , hyperpolarization-activated, cyclic nucleotide-gated (hcn) channels. should noted grouping functional rather evolutionary.

cyclic nucleotide-gated channels: family of channels characterized activation either intracellular camp or cgmp. these channels permeable monovalent cations such k , na. permeable ca, though acts close them. there 6 members of family, divided 2 subfamilies.
hyperpolarization-activated cyclic nucleotide-gated channels


temperature-gated channels: members of transient receptor potential ion channel superfamily, such trpv1 or trpm8, opened either hot or cold temperatures.

classification type of ions

chloride channels: superfamily of channels consists of approximately 13 members. include clcs, clics, bestrophins , cftrs. these channels non-selective small anions; chloride abundant anion, , hence known chloride channels.
potassium channels

voltage-gated potassium channels e.g., kvs, kirs etc.
calcium-activated potassium channels e.g., bkca or maxik, sk, etc.
inward-rectifier potassium channels
two-pore-domain potassium channels: family of 15 members form known leak channels, , display goldman-hodgkin-katz (open) rectification.


sodium channels

voltage-gated sodium channels (navs)
epithelial sodium channels (enacs)


calcium channels (cavs)
proton channels

voltage-gated proton channels


non-selective cation channels: these non-selectively allow many types of cations, na, k , ca, through channel.

most transient receptor potential channels



classification cellular localization

ion channels classified according subcellular localization. plasma membrane accounts around 2% of total membrane in cell, whereas intracellular organelles contain 98% of cell s membrane. major intracellular compartments endoplasmic reticulum, golgi apparatus, , mitochondria. on basis of localization, ion channels classified as:

plasma membrane channels

examples: voltage-gated potassium channels (kv), sodium channels (nav), calcium channels (cav) , chloride channels (clc)


intracellular channels, further classified different organelles

endoplasmic reticulum channels: ryr, serca, orai
mitochondrial channels: mptp, katp, bk, ik, clic5, kv7.4 @ inner membrane , vdac , clic4 outer membrane channels.



other classifications

there other criteria ion channel classification, including multiple pores , transient potentials.

almost ion channels have single pore. however, there 2 pores:

two-pore channels: two-member family thought form cation-selective ion channels. appear contain 2 kv-style six-transmembrane domains, suggesting form dimer in membrane. these channels related cation channels of sperm and, more distantly, trp channels.

there channels classified duration of response stimuli:

transient receptor potential channels: group of channels, referred trp channels, named after role in drosophila visual phototransduction. family, containing @ least 28 members, diverse in mechanisms of activation. trp channels remain constitutively open, while others gated voltage, intracellular ca, ph, redox state, osmolarity, , mechanical stretch. these channels vary according ion(s) pass, being selective ca while others less selective cation channels. family subdivided 6 subfamilies based on homology: canonical trp (trpc), vanilloid receptors (trpv), melastatin (trpm), polycystins (trpp), mucolipins (trpml), , ankyrin transmembrane protein 1 (trpa).




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