Protein Angst

Thursday, March 17, 2005

Hearts and Minds

I want you to take a look at the cardiac action potential. That right there is why your heart keeps on beating properly.

The action potential is an electrical pulse that stimulates the heart cells to beat. It travels from cell to cell like a Girl Scout selling cookies. When Little Miss Action Potential rings a heart cell's doorbell, though, she really upsets the natural order of things.

You see, a heart cell has a resting membrane potential. If you measured it with an electrode, it'd be negative. That's what you see in Phase 4 on that plot, which is graphing voltage over time.

The action potential makes it positive, and chaos ensues.

First of all, sodium channels open because they're designed to open at a positive voltage, and now sodium ions flow into the cell. Sodium ions, as you may know, are positive. So now the cell is becoming even more positive, as you can see in Phase 0.

"This is crap!" says the cell. Well, not really, because cells can't talk. But what I love about nature is that everything loves balance, everything loves the status quo, and when that balance is upset, it will do its damndest to set things straight.

So before things get too ridiculously positive, the potassium channels open to let potassium ions flow out of the cell. Potassium ions, as you may know, are also positive. Too much positive charge coming in? Simple, shuttle out some positive charge of your own. It's beautiful. It's Phase 1.

Then you have Phase 2, also known as the plateau phase, cause...look. It's a plateau. During Phase 2, sodium, calcium, and potassium ions are all in balance. There's very little inward or outward current here. It's like the channels are all waiting to see who'll make the first move. It's high noon at the Cardiac Corral.

And then Phase 3 hits. A couple very important potassium channels open, like, "The hell with it, the voltage is going back to normal RIGHT NOW." Except they're right on cue. If they were too early or too late, your heart would beat improperly and you would die, and dying is no fun.

All that happens during one action potential. One heart beat. Ion channels opening, closing. Ions going in and out of the cell. All day, every day, 24/7. It's a good thing ions don't get tired. Right now, they just did all that. Oh, look, they just did it again. And again. And again. And—hey, they took a second off. Dude, are you all right?



  • Does this happen in all beating heart cells? I'm thinking about my baby's heart cells that were beating before they were really a heart. (I guess you can tell where my mind is these days.)

    I'm not suggesting you should have an answer to this, but I wonder what kicks off the electric impulse in the first place. What makes that very first balanced cell become positive?

    Also, I didn't comment before, but thanks for posting the infant AIDS info before. It was interesting and I enjoyed reading it.


    By Anonymous Anonymous, at 8:13 PM  

  • I have a question that isn't about the heart, but does relate to one of your earlier articles. A friend recently told me that there might be a connection between people who survived the bubonic plague, and decendance of those people today having an immunity to AIDS. Is this true?

    By Anonymous Anonymous, at 12:18 PM  

  • Yes, it is. Click the link in that post; it's to an article I wrote that mentions several such connections.

    By Blogger Polter-Cow, at 4:53 PM  

  • Polter-Cow, just wanted to say I enjoyed reading your science articles. Have you thought of trying for the UC Santa Cruz Science Writing program? ( Or perhaps, like me, you've had just about enough of school for a while.

    I won't ask you to explain disordered proteins for your next article.

    Any articles in the works?

    By Blogger jesstone, at 2:12 PM  

  • Aww. My cells are AWESOME! I wonder if they appreciate that I know more about them now. I hope they do. And that they know they have you to thank for that.

    By Blogger Syd/GP, at 12:47 PM  

  • Dude, if you could write a Biology for Dummies book just like that, I could've understood Cellular Processes so much better. Where were you?

    By Anonymous ora_wai, at 10:56 AM  

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