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Thread: Voltage/Ligand-Gated Ion Channels and G-Coupled Protein Receptors

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    Voltage/Ligand-Gated Ion Channels and G-Coupled Protein Receptors 
    #1
    Bluelighter Ho-Chi-Minh's Avatar
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    Can someone explain the difference function between these two broad groups? Also, why is 5-HT3 a ligand-gated ion channel while all the other 5-HT receptors are g-coupled protein receptors? Thanks.

    Meant to say G-Protein Coupled receptors.
    Last edited by Ho-Chi-Minh; 26-03-2013 at 20:43.
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    Quote Originally Posted by Ho-Chi-Minh View Post
    Can someone explain the difference function between these two broad groups? Also, why is 5-HT3 a ligand-gated ion channel while all the other 5-HT receptors are g-coupled protein receptors? Thanks.

    Meant to say G-Protein Coupled receptors.
    A ligand gated ion channel is activated by a ligand, an exogenous drug or an endogenous transmitter (i.e. 5-HT3 opens in response to 5-HT). Voltage gated ion channels are activated by changes in the cellular membrane potential, but not ligands (i.e. sodium channels along the axon open in response to the voltage change produced by an action potential).

    Ion channels produce their signal much more quickly than GPCRs and the signal can be terminated much more quickly. 5-HT3 probably regulates processes that need better temporal control than a GPCR would allow, although I don't have any evidence for that.
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    Bluelighter Ho-Chi-Minh's Avatar
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    What do you mean by "cellular membrane potential"? As in an electrical pulse permeating through cells? I thought that's what ligands created.

    What does the "G" stand for in GPCR? And I'm assuming the "Protein" is the site at which the ligand binds?

    Thanks for the answer

    I'm a layman trying to get a decent understanding of psychopharmacology.
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    Quote Originally Posted by Ho-Chi-Minh View Post
    What do you mean by "cellular membrane potential"? As in an electrical pulse permeating through cells? I thought that's what ligands created.

    What does the "G" stand for in GPCR? And I'm assuming the "Protein" is the site at which the ligand binds?

    Thanks for the answer

    I'm a layman trying to get a decent understanding of psychopharmacology.
    It's the difference in voltage between the inside and the outside of the cell:

    http://en.wikipedia.org/wiki/Membrane_potential

    Ligands don't create the membrane potential, they can only raise and lower it. GPCR = G-protein coupled receptor, in other words a receptor coupled to a G-protein. G-protein is shorthand for guanine nucleotide-binding protein. So no the "protein" refers to the G-protein, inside the cell, ligands bind to the "R".
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    Perhaps not exactly what information is requested also, but GCPRs can also couple to different G-proteins for the same receptor and thus change effector. The entire system is certainly NOT as helpful as a simple /ligand vs voltage vigand distinction allows for.

    Just hope thats of use, since I've been studying GCPRs of late.
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    Quote Originally Posted by Limpet_Chicken View Post
    Perhaps not exactly what information is requested also, but GCPRs can also couple to different G-proteins for the same receptor and thus change effector. The entire system is certainly NOT as helpful as a simple /ligand vs voltage vigand distinction allows for.

    Just hope thats of use, since I've been studying GCPRs of late.
    That's a good point too, much more complexity with GPCRs than ion channels. I should also mention that GPCRs desensitize a lot more readily than ion channels, so the response from an ion channel is going to be a lot more stable and constant over time.
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    Bluelighter Ho-Chi-Minh's Avatar
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    As in drugs which agonize GABA-A and the nicotinic acetylcholline receptor will produce tolerance more slowly than those which agonize GABA-B and the muscarinic acetylcholline receptor?
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    #8
    The difference between them is their downstream effects. When ligand gated ion channels are opened up by an appropriate ligand (endogenous or exogenous drug) they'll let in ions for a period of time. These can be either positively charged or negatively charged, such as Ca2+ or Cl-. Normally a cell will has an inner membrane resting potential of around -70mV, when more positive ions are brought into the cell it's charge will become more positive (depolarize), making it more likely to fire an action potential. Negative charged ions are going to make the cell more negative (hyperpolarized), making it less likely to fire (inhibition).

    GPCRs on the other hand work through signalling cascades. When a ligand binds to a GPCR, depending on the subunits, its going to activate different messenger systems in the cell, which can all alter cell function. For example, increasing/decreasing transcription of a gene.
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    #9
    Bluelighter Ho-Chi-Minh's Avatar
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    Someone answer please. I want to get this down.
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    #10
    http://en.wikipedia.org/wiki/Synapse
    http://en.wikipedia.org/wiki/Neuron
    http://en.wikipedia.org/wiki/Neurotransmitter_receptor



    You should do your own reading first, ADD is intended for discussions about theoretical topics that you can't just look up on Wikipedia in 20 seconds.

    4 - Don't post things that don't belong here
    This forum was created to discuss things which don't fit in any other. Examples of things we want to see are:
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    #11
    Bluelighter Ho-Chi-Minh's Avatar
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    I did, in fact.

    You think it would take twenty seconds to learn what's been told?

    Bullshit. I don't need your scolding.
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    #12
    Bluelighter specialspack's Avatar
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    Quote Originally Posted by TCMVegas View Post
    You should do your own reading first, ADD is intended for discussions about theoretical topics that you can't just look up on Wikipedia in 20 seconds.
    Actually, ADD has slipped quite a lot (for better or worse) from those initial ideals. Certainly moderation here allows these type of educational threads.

    There's much less journal discussion these days from when it started, which is a shame. But I think these threads are useful too for helping people learn and to work through ideas that might be basic to some is always useful revision.

    On the other hand...

    Quote Originally Posted by Ho-Chi-Minh
    Someone answer please. I want to get this down.
    Dude - show a little patience. This forum isn't here just to spoon-feed you either.
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    #13
    Bluelighter specialspack's Avatar
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    Quote Originally Posted by St3ve View Post
    GPCRs on the other hand work through signalling cascades. When a ligand binds to a GPCR, depending on the subunits, its going to activate different messenger systems in the cell, which can all alter cell function. For example, increasing/decreasing transcription of a gene.
    GPCRs can also activate (or deactivate) ion channels by phosphorylation etc. They just do so over a broader temporal and spatial area, and are thus more modulatory than the more specific location and faster ligand gated ion channels.
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