QUESTION 16 Ion A+ and ion B+ are both permeable to the cell...

QUESTION 16 Ion A+ and ion B+ are both permeable to the cell membrane and exist in the following internal and external concentrations: A+ B+ Internal concentration (mM): 12 210 External concentration (mM): 120 50 If the membrane is 20 times more permeable to A+ than B+, what is the voltage across the membrane at rest (in mV, to the nearest 0.1)? QUESTION 17 Consider the same cell as in Question 16, with the permeable ions A+ and B+. What will happen to the cell's resting membrane voltage if the internal concentration of A+ is decreased? Vm at rest will increase Vm at rest will decrease Vm at rest will not change

Transcript

00:02 Our problem prompts us to consider a membrane with two cations across it.

00:11 We have an internal concentration of cation a of 12 and an external concentration of 120, and an internal concentration of cation b equaling 210 and an external of 50, so i have written that info out.

00:30 We are also told that the relative permeability of a is 20 times the relative permeability of b.

00:42 So we could even say, well, permeability of a equals 20.

00:48 We'll just call it 20.

00:50 And then permeability of b equals 1.

00:55 We don't know exactly what they are, but what? what matters is the relative value.

01:01 And we're asked to calculate the resting membrane potential across this membrane.

01:08 So when we're dealing with two or more ions, excuse me, two or more ions, we will want to use the goldman -hodgkin -cats equation.

01:22 And that is, it looks kind of scary, but, but, much of this is actually predetermined.

01:32 These three numbers or these three letters represent constants, meaning that in a given experimental setting, they don't change.

01:43 This is called the, you'll write this out.

01:47 This is the gas constant.

01:51 This is the temperature in the experimental environment in kelvin's.

02:01 This is the faraday constant, which just is constant.

02:06 It doesn't change.

02:08 Faraday.

02:10 I think i'm spelling that, right? and then we'll run the natural log of this mess.

02:19 So we have the permeability of a, multiplied by the external concentration, plus permeability of b, times the external concentration of b, and then all over permeability of a times internal concentration of a plus the permeability of b times the internal concentration of b.

02:42 And i could do this with calculator and whatnot, but instead i think we will plug in the numbers here on paper, digital paper, and then we're going to plug those same numbers into a calculator for us.

02:59 And i have one pulled up.

03:01 The web address is this, wikicalculator .com, and then you'll search for the goldman or ghk equation.

03:15 And so let's go ahead.

03:18 I'm going to pull up both screens together.

03:21 Come on, perhaps.

03:23 Come on.

03:28 All righty.

03:30 So our, and the ghk equation is set up for potassium, sodium, sodium, and chloride, because those are the major physiologic ions in our bodies.

03:43 But we could call k -a and n -a -b and just leave out chloride, and it will work just fine.

03:52 So let's say p of k, so p of a is going to be 20, and then p of b will be one, p of cl, we're just going to say zero.

04:14 So a's external concentration is 120.

04:23 B's external concentration is 50.

04:31 C is going to be zero.

04:36 A internal will be 12...

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