WOLFRAM|DEMONSTRATIONS PROJECT

Nernst Equation for Cellular Membranes

​
temperature (°K)
310
Potassium
[​
+
K
SubscriptBox[\(]\), \(\( \)\(outside\)\)]​
140
[​
+
K
​]​
inside
5
Sodium
[​
+
Na
SubscriptBox[\(]\), \(\( \)\(outside\)\)]​
15
[​
+
Na
​]​
inside
145
Chlorine
[​
-
Cl
​]​
outside
4
[​
-
Cl
​]​
inside
110
Calcium
[​
2+
Ca
​]​
outside
0.0001
[​
2+
Ca
​]​
inside
5
The Nernst equation is used to determine the potential of an ion of charge
z
across a membrane using both extracellular and intracellular concentrations. It can be written as
E
m
=
RT
zF
ln
[C]
i
[C]
o
, with
RT
F
=0.0000860
.
E
m
is the equilibrium membrane potential in volts;
R=8.3144621
Joules
Kelvin·Mole
is the ideal gas constant;
T
is the temperature in Kelvin;
F=0.00096485339
Coulombs
Mole
is Faraday's constant;
[
+
K
]
outside
,
[
+
Na
]
outside
,
[
-
Cl
]
outside
, and
[
2+
Ca
]
outside
are the extracellular concentrations of potassium, sodium, chlorine, and calcium ions;
and
[
+
K
]
inside
,
[
+
Na
]
inside
,
[
-
Cl
]
inside
, and
[
2+
Ca
]
inside
are the intracellular concentrations of potassium, sodium, chlorine, and calcium ions.
The default setting of the Demonstration calculates the equilibrium potentials for ions in a mammalian cell.