Ion Channel Blocker and Opener – Biological Membranes

by Kevin Ahern, PhD

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    00:00 is made.

    00:01 Now ion channels, I hope I've convinced you, are pretty important things. And we can imagine that blocking ion channels might have some significant impacts for cells, and they do.

    00:13 Some of these molecules, they are molecules that can block channels and the consequence of blocking can have some very significant impact. The neurotoxic alkaloids for example, an example of which is saxitoxin, that you can see on the right, is produced by paralytic shellfish toxin. What it does is, it blocks sodium channels of neurons, and can cause some significant damage, if not death as a result of its actions. Another common neurotoxin that blocks ion channels is tetrodotoxin. Tetrodotoxin is the toxic substance produced by puffer fish that is a delicacy in Japan. You eat the wrong part of a puffer fish and you're in trouble because it blocks the voltage-gated sodium channels of nerve cells.

    00:56 Now not all ion channel blockers are toxic, and if used properly they may have medicinal purposes. For example people who have heart arrhythmias commonly are treated with mild doses of blocks, of blockers of ion channels, for either sodium or potassium, that are targeted for specific cells. The result of this action is to slow down spurious signals that are otherwise causing the heart to be arrhythmic, and the arrhythmia can go away. Another medicinal use of ion channel blockers is those of the antihypertension drugs that will block calcium channels.

    01:32 Now there are other things that can be channel openers. There are for example substances that will open up, in this case potassium channels, one of them you can see on the right, and that's minoxidil. Minoxidil is a vasodilator, and minoxidil is better known as the hair grow treatment, Rogaine, that stimulates the growth of hair cells.

    01:57 This substance acts as a vasodilator because it's actually opening potassium channels.

    02:03 There are drugs that are used that are also channel openers, and these include anticonvulsants as you can see here. Ionophores are molecules that are related to channel proteins that we talked about here, but they're not proteins. These are lipophilic substances that in many cases are actually synthesized by organisms. Now these substances include potassium ionophores that will embed themselves in membranes and selectively allow potassium to move. One of the examples that you can see here is valinomycin shown on the right. It has a relatively simple structure and allows the movement of potassium into a cell. Valinomycin can act as an antibiotic because if it binds to a target cell and disrupts the cell's potassium gradient it can actually kill the cell.

    02:50 Proton ionophores are interesting and important. Now one of the really interesting ones here is called 2,4 Dinitrophenol or 2,4 DNP. Now 2,4 DNP first came into popularity about 100 years ago. Around the turn of the 20th century, there was a miracle diet drug that was released. The miracle diet drug was 2,4 DNP. And 2,4 DNP was advertised very much like the miracle diet drugs that you hear about today on the Internet. Those miracle diet drugs of course involve taking a pill and sleeping. While you sleep your fat burns away. Well it turns out that with 2,4 DNP, that actually did happen and the reason that happened was because the 2,4 DNP allowed protons to leak into the mitochondrion.

    03:36 Now we saw that the ATP synthase was relying on proton gradient, spinning that rotor to make the ATP. What if you poke a hole in the dam so the water, instead of going through the turbine, comes in through the hole? Well you will destroy the gradient, and if you destroy the gradient, what's going to happen to the synthesis of ATP? Well, of course it's going to plummet. Well cells need ATP, so when they need ATP, what do they start doing? They start burning substances like glucose, like fat, and so forth to generate the proton gradient. But the more they try to generate the proton gradient the more it simply leaks through the hole. 2,4 DNP was a miracle diet drug; it just killed a decent percentage of the people who took it. So I always tell students to think about this when I'm describing miracle diet drugs and so forth, and one of the questions I get from students after telling that story is the following, what if you took just a little bit? To which I say, well what if you took just a little bit of arsenic, would you do that? I don't think you would, so is not a good idea. In any event, 2,4 DNP is not something to mess with.

    04:44 Other things that are ionophores that are considerations are calcium ionophores. These include ionomycin, and there are other ionophores that will allow not just specific ions in, but a variety of ions in, and these include the compounds that you see on the screen here.

    04:59 Well I've spent a lot of time here talking about the importance of lipid bilayers, and the lipid bilayers as they relate to both the movement of ions, the generation of ATP, the control of the environment in which the cell exists. It's quite clear that the lipid bilayer is essential for a living cell, not only as a barrier against the rest of the world, but for carrying out the functions that a cell needs to perform.

    About the Lecture

    The lecture Ion Channel Blocker and Opener – Biological Membranes by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. They promote movement of ions across membranes
    2. They use triphosphate energy go move ions across membranes
    3. They help to build proton gradients
    4. They are not produced by living cells
    1. Valinomycin — an ion channel blocker produced by human cell to inhibit the movement of antibiotics across the cell membrane
    2. Saxitoxin — Na+ ion channel blocker in nerve cells
    3. Minoxidil — antihypertensive vasodilator medication
    4. Retigabine — anticonvulsant used in treatment for partial epilepsies
    5. 2,4-Dinitrophenol — a proton ionophore that dissipates the proton gradient across mitochondria membrane
    1. A proton ionophore that can shuttle protons across biological membranes and disrupt the proton gradient across them
    2. An ion channel blocker for the movement of sodium ions across the mitochondrial membranes
    3. A multiple ion channel blocker for the movement of various ions across the cell membrane, mitochondrial membranes and nuclear membranes
    4. An ion channel blocker for the movement of calcium ions across the nuclear membranes
    5. An ion channel opener for the movement of potassium ions across the cell membrane

    Author of lecture Ion Channel Blocker and Opener – Biological Membranes

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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