212,041 views
25 votes
25 votes
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: 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: Group of answer choices

User Chew Socks
by
3.3k points

1 Answer

12 votes
12 votes

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.

User Newbie Learner
by
2.3k points