However, this is not the full story. The SLC6 family, which is called “K+/Cl- dependent neurotransmitter transporter family”, contains the serotonin, dopamine and GABA reuptake transporters as well as 14 additional members, three of them with low sequence similarity and perhaps not acting as transporters (). One of them, , codes for a muscle-expressed acetylcholine/choline transporter () and another, , is expressed in the hypodermis and involved in an immunity response (its cargo is unknown) (). The remaining genes are completely uncharacterized, but two of them are expressed in neurons and six of them represent a nematode-specific gene expansion (). Any of these genes may encode reuptake transporters for known neurotransmitters systems for which no plasma membrane reuptake transporter has yet been identified (e.g., biogenic amines like tyramine, octopamine or trace amines), or for uncharacterized neurotransmitters.
Stomatins are membrane proteins thought to be auxiliary subunits that modulate the activity of DEG/ENaC/ASIC channels both in worms and vertebrates (). They are defined by the presence of a characteristic and structurally conserved core domain called the stomatin or SPFH domain (Stomatin, Prohibitin, Flotillin, HflK/HflC) domain. There are five mammalian stomatin genes and ten stomatin-like genes ( through ), most of them originating from an apparently nematode-specific expansion (). Even though only explicitly demonstrated to be an auxiliary subunit for / degenerin channels, the co-localization of protein with an innexin protein () suggests that stomatins may also be auxiliary subunits for different types of transmembrane channels (see for innexins). This is consistent with the physical association of vertebrate stomatin-like proteins with a TRP channel (). The expression patterns of five of the ten stomatins have been analyzed and neuronal expression was detected for each of them. The / DEG channel complex not only employs a stomatin as auxiliary protein, but also an oxidoreductase-related protein, MEC-14.
The Plasma Membrane | mybiochem
In vertebrates, the gap junction subunits are called connexins (20 in humans) and pannexins (three in humans), while invertebrate gap junction subunits are called innexins (; ). All proteins have a similar topology of four transmembrane domains with cytoplasmic N- and C-terminal tails. Vertebrate connexins and invertebrate innexins share no notable primary sequence similarity, but vertebrate pannexins (3 genes) were actually identified based on their similarity to innexins (hence the term “pannexin”).
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. The pore forming α subunit of both voltage-gated calcium and sodium channels contain 24 transmembrane (TM) domains which are 4 repeats of a 6TM motif thought to be derived from ancestral potassium channels () (). 6TM voltage-gated potassium channels, in turn, exist as tetramers, with the total ion channel therefore consisting also of a 24TM topology. Non-voltage-gated TRP channels and cyclic-nucleotide gated (CNG) channels—each of which also displays the 6TM topology—are related to these channels as well, as illustrated in (). These channels are described below in (potassium channels), (calcium channels), (TRP channels) and (CNG channels).
Cell Membrane Bubble Lab Revisited - Clear Biology
Plasma membrane-localized chloride channels are molecularly diverse and have many distinct functions in the nervous system. Besides the neurotransmitter-gated chloride channels mentioned above (), there are a number of additional chloride channels, some only recently identified as such (). In a good number of cases, the distinction between chloride channels and transporters is blurry.
Cell membrane - Cell Biology and Cytochemistry
Bestrophins are another family of plasma membrane-located, calcium-activated chloride channels (four genes in mammals) (). Bestrophins are expressed in multiple vertebrate tissue types including the nervous system. has significantly expanded its repertoire of these bestrophin-like genes: there are 26 family members, an expansion by a factor of more than six compared to mammals (). All proteins share a homology region (“Bestrophin” or “RFP-TM” domain) of 350-400 amino acids. Two of the three genes whose expression has been analyzed so far with reporter genes show expression in the nervous system ().