In this video we look at the mechanism by which the Sodium Calcium Exchanger works, to bring in three sodium ions to extrude one calcium ion.
Okay so welcome to this next video in the playlist on calcium signaling in this video what we’re going to do is we’re going to have a look at how this sodium calcium exchanger works in a bit more detail in ie how it manages to transport a cow’s warm calcium arm across the cell membrane in exchange for ota what if i’d done there that should be warm calcium not to
Calcium’s warm calcium you bring in three sodium ions and you extrude a single calcium and i do apologize for that in the previous video right so let’s have a look at how this protein actually works so basically this goes back to what we discussed in the first video of how pumps work so basically in order to have a pump you have to have two gates so a good cartoon
Model for this sodium sodium calcium exchange is we can draw a pore like so and then we’ll have a binding site basically what have some binding size in here and then we’ll have two gates okay right so initially what what to start with the situation we’ll start with is that the cytosol that gate is closed the extracellular gate is open and you now have calcium bound
To this site here so that’s where we’ll start we’ll start at this position here and we’ll get back to that position so it’s a great cycle so i will show how you get from this position to extruding the calcium and then back all the way to here okay so this is where we’re starting we have to start somewhere okay so this is the sodium calcium exchange lacuna so this
Is the m c x and the site extracellular gate here is open so let me color this in okay right so this here this blue gate here is the extracellular gate right so extracellular gate okay and you can also see on this picture that the cytosolic gate is closed so this down here is the cytosolic gate now just remove this up cytosolic gates that’s a solid key gate okay
Right so what’s going to happen is from now three sodium ions are going to come in and displace this calcium now they don’t all come in at once initially let’s draw these sodium ions here and that’s alicia lee what happens is that two sodium ions are going to come in from the extracellular fluid and they are going to displace the car some others these are going
To come in and basically what they’re going to do is they’re going to compete with the calcium ion for that binding site and the calcium ion is going to be released into the extracellular fluid so it’s going to go to this situation here so here’s the pore again here’s our binding sites now it has two of these little sodium ions bound to it instead of the calcium
The cytosolic eight is still closed and the extracellular gate is still open right so let’s color everything in so that everything’s nicely color-coded oh and the most important thing is that the calcium ion has now gone off into into the extracellular space so there’s our calcium gone and what we’re going to see without where this calcium came from okay so the
Calcium iron has gone with now displaced that calcium armed with these two sodium’s and what’s going to happen now is that another sodium iron is going to come in so the final sodium ion is going to come in now so we’ve got two already bound here comes the third can’t earn sodium and that’s going to come into the pour through the open extracellular gate like so and
It’s again going to bind to that binding sub site there the binding site here okay so when it binds to that binding site what’s going to happen is it’s going to trigger the closing of the extra center the game’s and then the opening of the site is onic gates and what’s gonna happen if i draw the next step over here so you have now three sodium ions announced that
A binding site here so here they are three of them bound and now the cytosolic gate has opened and the extracellular gate has closed right okay so cytosol ‘ok this is the extracellular gate over here closed now because the surface finding of these free sodium ions has changed the conformation now remember our calcium ion has now gone off it’s in the extra center
Compartment where we want it to be and i’m going to color code the cytosol that gate as well because why not so this pink is going to represent the cytosol occur gate here okay so here’s the cytosol it gate open now so in the cytoplasm what’s going to happen is that a calcium ion is going to come in so here’s our calcium ion again and now now that the protein has
Changed its conformation the affinity of the protein of this binding site for these sodium ions has changed basically and they were far prefer to be bound to calcium iron so what’s going to happen is that the calcium is going to come and displace those sodium ions so calcium is going to come in displace those sodium ions and the free sodium ions are going to go out
And what’s going to happen is that calcium is going to bind there the sodium ions have now gone out there in the in the cytosol now so they’ve gone into the intracellular compartment and what it’s going to trigger is when the calcium binds there it’s going to trigger another conformational change and so the cytosol that gate is going to close and the extracellular
Gate is going to open so what that will do is it will return you to this state over here basically so you will go back to the original starting position that we were at which was we have the extra send that gates open the site of got sonic a closed and a calcium ion bound to that binding site so you see now the importance of having these gains in the function that
This sodium calcium exchanger okay and the sodium calcium exchanger is really important for extruding calcium in tissues where you have very high transient calcium levels such as muscle cells and neurons
Transcribed from video
The Sodium Calcium Exchanger By Elliot Nicholson
