Complete question:
Suppose that the concentration of Na+ outside the cell is 100 and inside the cell is 10 mmol/liter. The Nernst equation at 20oC is:
Eion = 58 millivolts/z. [Log₁₀ (C-out/C-in)
You set the membrane voltage at +58 millivolts using a voltage clamp, and measure membrane current. If Na+ is the only ion crossing the membrane, you would expect to see:
a) 0 current
b) positive charges flowing into the cell
c) negative charges flowing into the cell
d) the membrane voltage becomes more positive
Answer:
b) positive charges flowing into the cell
Step-by-step explanation:
Nernst equation:
E = 58 millivolts/z. [Log₁₀ (C-out/C- in)
Where,
- E = Equilibrium potential
- 58 millivolts/z = Constant
- z = Ion charge + positive or negative symbol
- C-out = Ion concentration out of the cell
- C-In = Ion concentration inside the cell
The bigger concentration value places in the numerator and the smaller concentration value laces in the denominator.
Now let us see the provided values,
- z = Ion charge + positive or negative symbol ⇒ +1 ⇒ Na+
- C-out = Ion concentration out of the cell ⇒ 100 mmol/liter
- C-In = Ion concentration inside the cell ⇒ 10 mmol/liter
E = 58 millivolts/z. [Log₁₀ (Ion out/Ion i)
E = 58 millivolts/+1. [Log₁₀ (100mmol/liter / 10 mmol/liter)
E = 58 millivolts (Log₁₀ 10)
E = 58 millivolts (1)
E = 58 millivolts
58 mV is the absolute value of equilibrium potential.
Due to the differences in concentration, and being the only ion crossing the membrane, Na+ diffuses from outside -which is the highest concentration side- to the interior of the cell -which is the lowest concentration side-. Positive charges are moving into the cell. The interior of the cell becomes more positive.