Quick Question about Membrane Potential

[Ascleoius]

Hello all,
Good evening!

I have a quick question about membrane potential when I came across the following question:

Q: For most cells, extracellular calcium concentration is around 10,000 times higher than the intracellular calcium concentration. what is the membrane potential established by this electrochemical gradient?
A: V=(61.5/2)* log (10^4/1)= 123mV according to the Nernst equation.

I am just thinking why is the voltage inside of the cell positive 123mV when there is more Ca^2+ outside of the cell? If there is more positive ions extracellular, wouldn't the voltage of the cell negative instead?
Please help me and thank you so much in advance.

---

Members don't see this ad.

 

[Pono_0001]

I'm not sure why you'd think more positive ions extracellular= negative equilibrium potential for that ions. but really there's nothing to understand in this case. it's like we decided north is up in the map instead of south is up. physiologist early on decided the convention and it's reflected in the equation. keep in mind that you'll have to use another equation to calculate the membrane potention as there'll likely be more than one ion involved. maybe that's where your confusion's from?