Talk:Voltage clamp
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I've moved this page from Electrophysiology, which I thought was too long. I've been working to clean it up, but it still needs work. Here's some material that I took off the page because I thought it was too informal and maybe not necessary. delldot | talk 04:08, 25 November 2005 (UTC)
Say you are standing at the bottom of a hill holding a soccer ball. You have a friend standing up on the hill who wants the ball. The friend can move up and down the hill at will. Your friend, or more accurately, the altitude of your friend, is the command potential. The altitude of the soccer ball is the cell’s membrane potential. The difference between the altitude of your friend and the altitude of the ball is the error signal. You are the electrode.
In discontinuous single-electrode ball movement, you move the ball up the hill with your feet. You cannot judge the distance to your friend and see the ball at the same time (say you have to look down to see the ball, and up to see your friend). So you judge the distance to your friend (measure the voltage difference) then kick the ball toward your friend (an epoch of current passing). The distance is too great to make it to your friend in one kick, so you run up the hill after the ball, (entering the next duty cycle) judge the distance again and kick the ball up the hill again. You repeat this until the ball reaches your friend (and thus, the error signal is zero). Now, if the speed at which you can run up the hill is too slow compared to the ball’s speed at rolling back down the hill, you won’t make any progress. But if you are significantly faster than the ball, you can run up the hill, and kick it again before it’s had much of a chance to roll back down the hill. This is basically what is happening during SEVC-d. The electrode is kicking the cells membrane potential toward a goal, pausing to measure the voltage, and then kicking it again before it can decay significantly. Of course, such analogies can go only so far in explaining. Here for instance, it doesn’t really need to be your friend on the hill. It could just as well be your enemy (although why you’d want to give your enemy a soccer ball is beyond me). But your enemy might want to torment you by constantly changing the command potential, so maybe its better if you stick with a friend.
Just to carry this analogy to its logical extreme, two electrode voltage clamping would be the same, except you could just carry the ball up the hill without ever taking your eyes off of your friend. SEVC-c would be like giving the ball to a little kid who you ‘’think’’ is reliable, but you’re not completely sure, and asking the kid to carry the soccer ball to your friend. You lost your glasses, so you can only kind of see the kid, so you think he’s doing the job, but you are not really sure.
