Question

1) The concentration of K⁺ outside of a cell is 300 mM, and the concentration inside the cell is physiologically normal. The V_m for this cell will be:

1. -80 mV
2. close to +29 mV
3. more positive than -80 mV
4. more negative than -80 mV
5. b and c

Answer 1

Vm = RT/zF ln [K+]out/[K+]i

At body temperature,

R = 8.31 joule/degree K-mole

Temperature at 370C= 298.15 0K

F = 9.65 x 104 c/mole

z for potassium= 1

The Potassium concentration is normally atleast 20 times higher inside the cell as compared to outside. As outside potassium concentration is 300mM, the inside concentration will be 20 X 300 mM= 6000 mM.

Vm= 61.5 log 10 [K+]o/[K+]i

Vm= 61.5 X log 10 [300 mM]/[6000 mM]= 61.5 X [(log 300)- (log 6000)]

Vm= 61.5 X [2.478-4.78]= 61.5 X (-2.302)= -141mV

At 370C, the Vm=-141 mV

Vm cannot be negative as K+ is positively charged with concentration higher inside the cell.

Right choice: d. more negative than -80 mV