With different drugs, okay? So someone proposed use different drugs, okay? What kind of drugs? So you already have this very robust squid axon, and then you design this amplifier that can allow you to do this voltage jumping experimenet, and then you understand the passive property of the membrane. And this is just charging the capacity of the membrane. It exists for all passive membrane. But now to what you observe is something interesting. And you think those are gold mines and you observe that the current first go inward under this condition, and then somehow goes outward. And then you are asking yourself, hm, this is interesting. Why the current would go inward and outward? And specifically you are asking yourself what kind of ions mediate those current flow inward and outward? Apparently they should be different ions right, because if they are the same ions, it's the same voltage. If I look right here, it's the same voltage, okay? Once you have the same voltage, the direction of ion flow depends on the driving force, depends on how this voltage differs from this Nernst potential, different from the equilibrium potential, okay? If it's the same ion, then the difference will be the same. The driving force will be the same, so the direction will be unique, okay? And under this the same voltage and at least you will find that the two direction of current flow. One is inward and one is outward, so that indicates that there will be two different ionic sources, okay? Because if we use the same one, they should go to the same direction. So how do you sort out or determine what might be the ions going inward and what might be the ion going outward? And someone proposed using drugs, how specific drugs. What? Okay, so someone propose as you proposed something can specifically block the drugs from using our modern technology,oh, cool. We use pharmacology, use some toxin, okay? For example, TTX that we know can block voltage gating sodium channel. That's good, okay? Let's see, if you guys traveled back carrying the TTX, okay? And then do that experiment, great. what would be the current looks like after you apply TTX. So in this condition with TTX, The current looks like, Okay, maybe we draw it not to a same scale. So the initial ones goes away and the other one remain, and therefore you can draw the conclusion, well this will be the sodium current going inward, okay? But what if that you did not have TTX or you didn't know that such a drug exists? How do you determine what kind of current going inward and what kind of current going outward under this condition? Before we change our ions, let's think about, In fact before we change our ions, we can generate a certain prediction. We can generate prediction as what kind of current flow in which direction that it's going to be, okay? Because in our last discussion, we already mentioned that the different potassium and sodium concentration inside the cell and outside the cell are very different, okay? Sodium usually is high outside the cell and low inside the cell, so outside is 100 millimole or more, okay? And potassium outside a cell, so this is out, Is relatively low 3 to 4 millimole. While potassium inside it's much higher, okay? 140 millimole for example. for example, indeed. And sodium is relatively low. Indeed, actually, we know roughly the equilibrium potential for sodium and potassium inside the cell. That is if the sodium, if the potassium is in the equilibrium condition. Then the equilibrium potential for potassium is close to minus 80 millivolt, okay? All right? And sodium, the equilibrium potential based on our concentration, okay? Is about plus 40 or 50 millivolt, okay? So that is in a regular ionic composition condition. There is the reverse potential for potassium and the reverse potential for sodium, okay?
